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{{spading|Pokérus}}
[[File:Pokérus Adventures.png|thumb|right|230px|Pokémon infected with Pokérus in [[Pokémon Adventures]]]]
[[File:Pokérus Adventures.png|thumb|right|230px|Pokémon infected with Pokérus in [[Pokémon Adventures]]]]
The '''Pokérus''' (Japanese: '''ポケルス''' ''Pokérus''), from "Pokémon virus", is a microscopic life-form that may attach to {{OBP|Pokémon|species}}, first appearing in the [[Generation II]] {{pkmn|games}}.  
The '''Pokérus''' (Japanese: '''ポケルス''' ''Pokérus''), from "Pokémon virus", is a microscopic life-form that may attach to {{OBP|Pokémon|species}}, first appearing in the [[Generation II]] {{pkmn|games}}. It is a beneficial mechanic that a Pokémon can obtain.


==In the games==
==In the games==
<!--Do the nurse's comments differ between DPPt and HGSS?-->
When a Pokémon has the Pokérus, it gains double the [[effort values]] from battling (e.g., fighting a {{p|Magikarp}} will give two {{stat|Speed}} EVs, rather than one). Effort points gained from [[Vitamin]]s and [[Feather]]s are not doubled. The infected Pokémon can infect other Pokémon with the virus for a period of one to four days. However, the Pokérus timer can be delayed by several methods, such as by placing the infected Pokémon in a PC Box.
Unlike other [[status ailment]]s, Pokérus cannot be healed at a [[Pokémon Center]] or with any [[status ailment healing item]], and can only be obtained by the Pokémon in question once. When a Pokémon has the Pokérus, it gains double the [[effort values]] from battling (i.e., fighting a {{p|Magikarp}} will give two {{stat|Speed}} EVs, rather than one). Effort points gained from [[vitamins]] and [[wings]] are not doubled. The infected Pokémon can infect other Pokémon with the virus for a period of about two days. However, the Pokérus timer can be delayed by several methods including placing the infected Pokémon in a PC Box.


Pokérus has a 3 in 65,536 chance of being generated on a {{OBP|Pokémon|species}}, either {{pkmn2|wild}} or [[Pokémon breeding|bred]]. Through battling or capturing this wild Pokémon, {{player}}s could get this helpful virus onto their own Pokémon, and subsequently spread it around. Due to the overwhelmingly low chance of encountering the virus (about 1/3 of the chance to encounter a {{Shiny}} Pokémon), and the fact that most would not even recognize a Pokémon with the virus and may flee from it, many players would never have a Pokémon with the virus.
While it is represented similarly to [[status condition]]s, the Pokérus is not a status condition, so it cannot be healed at a [[Pokémon Center]] or with any [[status condition healing item]].


In later generations, the Pokérus became more accessible, with worldwide trading facilitated by the [[Nintendo DS]]'s Wi-Fi capabilities beginning [[Generation IV]]. In fact, it is common courtesy to infect Pokémon to be traded on the Global Trade Station with Pokérus within some parts of the fandom. Also, a Pokémon's chances of being infected with the virus very slightly increase when a Pokémon has been traded from another game.
Pokérus has a 3 in 65,536 (or approximately a 1 in 21,845) chance of being generated on one of the {{player}}'s Pokémon after a battle, making it rarer than encountering or hatching a [[Shiny Pokémon]]. If any of the player's Pokémon are infected, the Pokérus may spread among Pokémon in the player's party after any battle.
<!--Proof of this last statement, please? What's the higher 'rus chance?-->
 
From [[Generation IV]] onward, the Pokérus became more accessible, with worldwide trading facilitated by [[Nintendo Wi-Fi Connection]].


===Infection===
===Infection===
When infected, a Pokémon's status screen will indicate it much as it does any other status condition (with icons being different for Generation III and IV, while Generation V has the same as Generation IV and Gen II having no icon at all). When another normal status condition, such as {{status|Sleep}}, affects the Pokémon, the Pokérus icon will be replaced. As long as the Pokémon is infected with Pokérus, it can spread the virus to the other Pokémon in the player's party. The infection may spread if the infected Pokémon is in the main party after a battle. An uninfected Pokémon must be next to a Pokémon infected with Pokérus in the main party for the virus to spread. If Pokémon that have already been infected and cured from Pokérus are in the main party and are on either side of a Pokémon currently with the disease, Pokérus will not spread after any amount of battles. Pokémon that are put into the [[PC]] will keep the status indefinitely. From Generation III onward, {{pkmn|Egg}}s may catch Pokérus like any other Pokémon.
When a Pokémon is infected with the Pokérus, their status screen will display an icon indicating this special "status" the same way status conditions would be noted. If the Pokémon becomes affected by a status condition such as {{status|Sleep}}, the Pokérus icon will be temporarily replaced until the status condition is cured. As long as the Pokémon is infected with the Pokérus, it can spread the virus to other Pokémon in the player's party.
 
The Pokérus may spread if an infected Pokémon is in the player's party after a battle. The Pokérus may only spread to a Pokémon directly adjacent to an already infected Pokémon, and only if they have never had Pokérus before. {{pkmn|Egg}}s may catch the Pokérus like any other Pokémon.
 
===Becoming cured===
A Pokérus infection only progresses towards cured status when a new day starts with the infected Pokémon in the party (or if, when the game is loaded, it is not the same day as it was when the game was saved). The number of days before a Pokémon will be cured of the Pokérus can vary from one to four days. Once this time has passed, the Pokémon becomes cured and will be immune to the virus in the future. The Pokémon still gains double effort values when cured.
 
Due to the beneficial nature of the Pokérus, players will often place an infected Pokémon in the [[PC]] where it will keep the infection indefinitely, so that it may be withdrawn to spread the virus at will. Other options include putting a Pokémon in the {{pkmn|Day Care}} or sending it to {{pkmn|Stadium 2}} in [[Generation II]], {{g|Box Ruby & Sapphire}} in [[Generation III]], [[My Pokémon Ranch]] in [[Generation IV]], [[Pokémon Bank]] in [[Generation VI]] and [[Generation VII]], or [[Pokémon HOME]] in [[Generation VIII]].
 
In Generation III, if the player deposits an infected Pokémon inside a PC, saves inside a Pokémon Center prior to midnight, shuts off the game, resumes the game after midnight, withdraws the infected Pokémon from the PC, and exits the Pokémon Center, it is possible for the infected Pokémon to be cured of the Pokérus upon stepping outside of the building. This does not happen in any other generation.
 
In Generation VIII, the game will check on the next available random event increment after midnight. This can result in a Pokémon that was infected while in a box, and withdrawn directly after resuming the game from sleep, being subsequently cured of the Pokérus after the next battle or similar event.
 
====Technical information====
The Pokérus is stored in a Pokémon's [[Pokémon data structure|data structure]] as a single byte. In hexadecimal, this can be represented as a two-digit number '''XY'''. The upper 4 bits of the byte, '''X''', represent the specific strain of the Pokérus the Pokémon has contracted. The lower 4 bits, '''Y''', represent the number of days remaining before the infected Pokémon is cured of the virus.
 
A Pokémon is or has been infected if '''X''' (the strain) is a nonzero value. If '''Y''' (days remaining) is nonzero when '''X''' is also nonzero, this means the Pokémon is currently infected. If '''Y''' is 0 and '''X''' is nonzero, then the Pokémon is "cured" of the Pokérus. If both '''X''' and '''Y''' are 0, then the Pokémon has never been affected by the Pokérus.
 
Whenever the game's internal clock strikes midnight, every currently infected Pokémon in the player's party has their Pokérus value decreased by one. Once the '''Y''' value reaches 0, the Pokémon will be cured of the Pokérus.
 
=====Strains=====
Whenever the game creates the Pokérus on a Pokémon, the value assigned to '''Y''' (days) depends on the value assigned to '''X''' (strain). Specifically, the number of days will be set to '''X''' modulo 4 + 1. In other words, the higher two bits of '''X''' are irrelevant to the "strain".
{| class="roundy" style="text-align:center; border: 3px solid #A54ACE; background: #D67BFF"
! style="background: #EFA5EF; {{roundytl|5px}}" | Strain
! style="background: #EFA5EF" | X values
! style="background: #EFA5EF; {{roundytr|5px}}" | Duration<br>(Y value)
|- style="background: #fff"
| A || 0, 4, 8, 12 || 1 day
|- style="background: #fff"
| B || 1, 5, 9, 13 || 2 days
|- style="background: #fff"
| C || 2, 6, 10, 14 || 3 days
|-
| style="background: #fff; {{roundybl|5px}}" | D
| style="background: #fff" | 3, 7, 11, 15
| style="background: #fff; {{roundybr|5px}}" | 4 days
|}
 
Whenever the Pokérus spreads from an infected Pokémon to a new Pokémon, the new Pokémon inherits the infected Pokémon's strain of the Pokérus ('''X''') and '''Y''' is copied directly from the infected Pokémon. As an example, if a Pokémon has the Pokérus with an '''X''' value of 7 and a '''Y''' value of 2 (2 days remaining before it will be cured) and it infects another Pokémon, the new Pokémon will be infected with Pokérus with an '''X''' value of 7 and a '''Y''' value of 2. Infecting other Pokémon does not reset the '''Y''' value to the default value for a given strain on the newly infected Pokémon, nor for the original host.
 
In {{g|Emerald}} onward, '''X''' values of 0 and 8 do not generate legitimately, as the [[RNG]] doesn't permit these values to generate. Additionally with a value of 0, upon being "cured" the Pokémon would appear to have never had the Pokérus at all.


===After having the virus===
===After having the virus===
Once a Pokémon's immune system has fought off the virus, they cannot spread it further, nor can it be spread to them by other Pokémon. In Generations II and III, a dot will appear on the Pokémon's status screen to indicate that they have had the virus previously, while in Generation IV and V, it will be a small smiley face. Though the virus is gone, its positive effects will remain, most specifically the ability for that Pokémon to gain double {{EV}}s.
Once a Pokémon's immune system has fought off the virus, they cannot spread it further, nor can it be spread to them by other Pokémon. In Generations II and III, a dot will appear on the Pokémon's status screen to indicate that they have had the virus previously, while in Generation IV and onward, it will be a small face. Though the virus is gone, the Pokémon will still gain twice the {{EV}}s it would have gained before the virus.


Any Pokémon on the player's party at the moment the system clock reaches midnight after a certain number of days in that position (number of days depends on the strain and generation) will become immune. An easy way to keep a "vessel" for future spreading is to always send the infected Pokémon to the PC, {{pkmn|Day Care}}, {{pkmn|Stadium 2}} (in [[Generation II]]), {{g|Box Ruby & Sapphire}} (in [[Generation III]]), or [[My Pokémon Ranch]] (in [[Generation IV]]) before midnight. The game also recognizes immunizing if the system is turned off and on again on the next day.
===Differences between generations===
====Generation II====
When the player first encounters the virus in one of the [[Generation II]] games, the [[Pokémon Center lady]] at the [[Pokémon Center]] will make note of it when the Pokémon is first healed after contracting it, saying that there are "tiny life forms" on the Pokémon. After leaving the Pokémon Center, [[Professor Elm]] will call the player to tell them that the virus has no effect and will wear off. A Pokémon with active Pokérus will list its status as such, and a Pokémon that has had the Pokérus and is cured will have a small dot near its HP meter on the status screen. At the end of a battle, the virus has a 1/3 chance to spread. If the infected Pokémon is adjacent to two Pokémon who have never had it before, one of them will catch the Pokérus. Pokérus can infect {{pkmn|Egg}}s as well. An indicator for Pokérus will not show up on the {{pkmn|Egg}}'s status screen, but once it hatches, it will appear under its status on the status screen like normal.


===In Generation II===
If a Pokémon with any stage of the Pokérus (active or cured) is traded back to a [[Generation I]] game, or withdrawn from [[Pokémon Stadium 2]] by a Generation I game, all traces of that Pokémon having had the Pokérus will disappear. This is because a Pokémon's Pokérus status is not saved in any form in the Generation I games, thereby making it possible for a Pokémon to legitimately contract the Pokérus multiple times by trading it back and forth, once it becomes cured of a given infection. The only benefit of doing so would be to allow other Pokémon to contract the virus.
When the player first encounters the virus in one of the [[Generation II]] games, the nurse at the [[Pokémon Center]] will make note of it when the Pokémon is first healed after contracting it, saying that there are "small life forms" on the Pokémon. After leaving the Pokémon Center, [[Professor Elm]] will call the player to tell them that the virus has no effect and will wear off. A Pokémon with active Pokérus will list its status as such, and a Pokémon that has had Pokérus and is cured will have a small dot near its HP meter on the status screen.
====Nurse's comments====
"''Your <sc>Pokémon</sc> appear to have tiny life forms stuck to them.<br> Your <sc>Pokémon</sc> are healthy and seem to be fine.<br> But we can't tell you anything more at a <sc>Pokémon Center</sc>.''"
====Elm's explanation====
''"Hello, <player>?<br>I discovered an odd thing.<br>Apparently there's something called <sc>Pokérus</sc> that infects <sc>Pokémon</sc>.<br>Yes, it's like a virus, so it's called <sc>Pokérus</sc>.<br>It multiplies fast and infects other <sc>Pokémon</sc> too. But that's all.<br>It doesn't seem to do anything, and it goes away over time.<br>I guess it's nothing to worry about. Bye!"''


====Technical information====
The Pokérus cannot randomly occur before the player has visited [[Goldenrod City]]<ref>[https://github.com/pret/pokegold/blob/74bffc2c8dd0b5b1873e51bc53e83177f35f7020/engine/events/pokerus/pokerus.asm#L19-L20 pret/pokegold: pokerus.asm lines 19-20]</ref> (but it may spread between Pokémon before then). If a Pokémon in the party has the Pokérus, other Pokémon cannot randomly contract it; they can only receive it from that Pokémon.<ref>[https://github.com/pret/pokegold/blob/74bffc2c8dd0b5b1873e51bc53e83177f35f7020/engine/events/pokerus/pokerus.asm#L7-L10 pret/pokegold: pokerus.asm lines 7-10]</ref>
In [[Generation II]], Pokérus is stored in a Pokémon's [[Pokémon data structure in Generation II|data structure]] as a single byte at offset 0x1C. Within the byte, the upper 4 bits (upper nibble) and lower 4 bits (lower nibble) are represented in hexadecimal format as '''XY''', where '''X''' represents the specific strand of Pokérus the Pokémon has contracted, and '''Y''' represents the number of days remaining before the infected Pokémon is cured of the virus.<br>
 
=====Infection and spread details=====
{{incomplete|section|needs=Description of the random byte generation algorithm, which is that used by other random byte-needing routines}}
The party is first iterated over to determine if any member has the Pokérus. If so, the spread code is called for each member with the Pokérus and not the new infection code, and if not vice versa.


This means that there exist 256 possible states of Pokérus: 1 unaffected state, 240 infected states (39 legitimate and 201 hacked), 15 cured states:
The spread code checks if a random byte is less than 85 and if the party has multiple members before proceeding as follows: if the spreader is the last party member, or if a random byte is less than 128, iterate backwards, otherwise iterate forwards. If the member being iterated over has an active infection, they are skipped over and become the spreader. If they are clear and never had the Pokérus, they are infected. The '''Y''' value for an infection is generated from the '''X''' value as it is for a spontaneous infection, unlike in future games where it is copied. The iteration stops when a member is newly infected, when it reaches a cured member, or when it would be about to pass through the beginning or end of the party.
* An unaffected state is always represented as 0 (hex 00).
* An infected state is represented by any number between 1 and 255 that has a remainder when divided by 16. In other words, when the lower nibble '''Y''' is nonzero, the Pokémon is infected.
** For example, 33 (hex 21) represents an infected state, since 33 divided by 16 would produce 1 as a remainder.
* A cured state is represented by any number between 1 and 255 that does not have a remainder when divided by 16. In other words, when the lower nibble '''Y''' is zero, the Pokémon is cured.
** Possible 'cured' values can be 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224 or 240 (hex values 10, 20, 30, 40, 50, 60, 70, 80, 90, A0, B0, C0, D0, E0 or F0 respectively).


=====Remaining days=====
The new infection code first checks if the flag for having visited Goldenrod City is set, terminating if not. Then, it checks if a random byte is equal to zero and another random byte is less than three, terminating if not. It then chooses a random party member by generating a random byte and keeping its bottom three bits (bitwise ''and'' with seven), rerolling until that number is a valid party index. If that party member has ever had the Pokérus, the code terminates. Otherwise, a random byte is rolled, rerolling if zero until not zero. This byte shall be represented as '''AB''' (not to be confused with registers A and B) in the same way that the Pokérus byte is represented as '''XY'''. If '''A''' is not zero, '''B''''s bottom three bits (bitwise ''and'' with seven) are copied as a four-bit value, incremented, and put into '''X''', and '''X''''s bottom two bits (bitwise ''and'' with three) are copied as a three-bit value, incremented, and put into '''Y'''. Otherwise, it is likely intended to copy '''B''' into '''X''', but, perhaps due to a misplaced load, zero is copied into '''X''' instead; '''Y''' is then derived from '''X''' with the same code as with '''A''' not zero, but since '''X''' is always zero, '''Y''' is always one. (If the misplaced load is placed in a more logical place, the '''Y''' value ends up always being one anyway, so there may have been more required effort to make the code work as intended.)
Whenever the game's internal clock strikes midnight, every Pokémon in the player's party has their Pokérus value decreased by one point. Once the '''Y''' value reaches 0, the Pokémon will be cured of Pokérus.<br>
For example, if a given Pokémon's Pokérus value was 65 (hex 41), it would decrease down to 64 (hex 40) and therefore be cured. However, if the value was 82 (hex 52), it would instead decrease down to 81 (hex 51). This means that if consistently left in the player's party, it is possible for a Pokémon to remain infected with Pokérus for a potential maximum of 15 days.


=====Specific strain=====
'''X''' values of zero and eight can occur naturally: the latter is as designed, the former is due to the above bug. Due to this bug, an '''X''' value above eight cannot occur naturally. Probabilities of each strain is as follows:
Whenever the game assigns a Pokérus value to any given Pokémon, '''Y''' values between 1 through 4 are used, depending upon the '''X''' value generated. (However, any '''Y''' value can be attained through hacking, meaning that if left in the player's party, a Pokémon can only remain infected with Pokérus for a legitimate maximum time span of 4 days.)


The value of '''X''' represents the specific Pokérus strain that the Pokémon has been infected with:
{| class="roundy" style="text-align:center; border: 3px solid #A54ACE; background: #D67BFF"
{| {{bluetable}}
! style="background: #EFA5EF" | X values
! style="background: #ccf" | Strand #<br>(X value)
! style="background: #EFA5EF; {{roundytr|5px}}" | Chance to occur
! style="background: #ccf" | Duration<br>(Y value)
|- style="background: #fff"
! style="background: #ccf" | Pokérus value
| 0 || 15/255<br>(5.88235%)
|- style="background: #fff"
| 1, 2, 3, 4, 5, 6, 7, 8 || 30/255<br>(11.76471%)
|-
|-
| 00 || 1 day || 001 (hex 01)
| style="background: #fff; {{roundybl|5px}}" | 9, 10, 11, 12, 13, 14, 15
| style="background: #fff; {{roundybr|5px}}" | 0/255<br>(Cannot naturally occur)
|}
 
====Generation III====
The Pokérus can only be contracted or cured in {{3v2|Ruby|Sapphire|Emerald}}. In {{2v2|FireRed|LeafGreen}}, as well as {{pkmn|Colosseum}} and {{Pokémon XD}}, since the [[time]] function is absent, a Pokémon with the Pokérus will keep it indefinitely (it can't spread the Pokérus, either)<!-- at least FRLG!-->, until it is transferred to the [[Hoenn]]-based games. When a Pokémon can spread the Pokérus, it has a 1/3 chance to spread it to both adjacent Pokémon.
 
Otherwise, the Pokérus operates in much the same way as in Generation II, but it is now possible for the Pokérus to be randomly contracted even when another Pokémon in the party already has it (and the Pokérus can spread after the same battle where it was contracted)<ref>[https://github.com/pret/pokeruby/blob/a3228d4c86494ee25aff60fc037805ddc1d47d32/src/battle_main.c#L5125-L5129 pret/pokeruby: battle_main.c lines 5125-5129]</ref>, and there is no location requirement before the Pokérus can randomly be contracted. Eggs infected with Pokérus will now indicate as such.
 
In {{2v2|Ruby|Sapphire}} only<ref>[https://github.com/pret/pokeruby/blob/a3228d4c86494ee25aff60fc037805ddc1d47d32/src/pokemon_3.c#L835-L853 Pokerus Logic in Ruby Disassembly]</ref>, '''X''' values of 0 and 8 do occur naturally, whereas in {{g|Emerald}} onward, the RNG does not allow them to occur at all. The following is the chance to obtain each strain in Ruby and Sapphire:
{| class="roundy" style="text-align:center; border: 3px solid #A54ACE; background: #D67BFF"
! style="background: #EFA5EF" | X values
! style="background: #EFA5EF; {{roundytr|5px}}" | Chance to occur
|- style="background: #fff"
| 0 || 30/255<br>(11.76470%)
|- style="background: #fff"
| 1, 2, 3, 4, 5, 6, 7 || 31/255<br>(12.15686%)
|-
|-
| 01 || 2 days || 018 (hex 12)
| style="background: #fff; {{roundybl|5px}}" | 8, 9, 10, 11, 12, 13, 14, 15
|-
| style="background: #fff; {{roundybr|5px}}" | 1/255<br>(0.39215%)
| 02 || 3 days || 035 (hex 23)
|-
| 03 || 4 days || 052 (hex 34)
|-
| 04 || 1 day || 065 (hex 41)
|-
| 05 || 2 days || 082 (hex 52)
|-
| 06 || 3 days || 099 (hex 63)
|-
| 07 || 4 days || 116 (hex 74)
|-
| 08 || 1 day || 129 (hex 81)
|-
| 09 || 2 days || 146 (hex 92)
|-
| 10 (hex A) || 3 days || 163 (hex A3)
|-
| 11 (hex B) || 4 days || 180 (hex B4)
|-
| 12 (hex C) || 1 day || 193 (hex C1)
|-
| 13 (hex D) || 2 days || 210 (hex D2)
|-
| 14 (hex E) || 3 days || 227 (hex E3)
|-
| 15 (hex F) || 4 days || 244 (hex F4)
|}
|}


For example, if a Pokémon has a Pokérus value of 50 (hex 32), meaning it has strain 3 and will be cured in 2 more days. If it were to infect another Pokémon, the new Pokémon would obtain the Pokérus value of 52 (hex 34), meaning it would instead be cured in 4 more days. The strain remains constant when copied over. The remaining number of days prior to being cured however, depends on the strain itself.
====Generation IV====
The mechanics remain the same from Generation III. Additionally, much like storage in {{g|Box Ruby & Sapphire}} and in the PC, storage in [[My Pokémon Ranch]] will keep a Pokémon's Pokérus status indefinitely. The Pokérus doubles the [[Effort value|EVs]] earned from [[Power item]]s.


Currently, there is no known way to determine how specific strains are generated by the game (other than the fact that there is a 3 in 65,536 chance of a wild Pokémon carrying Pokérus). However one of these 16 strains is illegitimate: Strain 0. This is because when Pokérus values between 1 through 15 (hexadecimals 01 through 0F) eventually decrease down to 0 (hexadecimal 00), a Pokémon would not only be cured of Pokérus, but would also lose any sign of having been infected in the first place—meaning that they could become reinfected at a later point in time.
In {{2v2|HeartGold|SoulSilver}}, [[Professor Elm]] calls the player soon after healing their first Pokémon with the Pokérus to tell them that it has no effect and will wear off. If he is called back, he will claim that Pokémon will level up better with the Pokérus while infected.


As a result, out of the 240 possible states of Pokérus infection, only 39 of them are considered legitimate. This can be calculated by adding up all of the 15 legitimate strains and multiplying each of them by the possible number of remaining infected days (2 + 3 + 4 + 1 + 2 + 3 + 4 + 1 + 2 + 3 + 4 + 1 + 2 + 3 + 4 = 39).
====Generation V====
The mechanics remain more or less the same, but now the icon that appears if a Pokémon has previously had the Pokérus is pinkish in color instead of the former yellow/orange color.


====Erasing Pokérus from a Pokémon====
=====Pseudorandom number generation=====
If a Pokémon with any stage of Pokérus (active or cured) is traded back to a [[Generation I]] game, or withdrawn from Stadium 2 by a Generation I game, all traces of that Pokémon having had Pokérus will disappear. This is because a Pokémon's Pokérus status is not saved in any form in the Generation I games, thereby making it possible for a Pokémon to legitimately contract Pokérus multiple times by trading it back and forth, once it becomes cured of a given infection.
To determine if any Pokémon in the player's party is to be infected, the game calls the {{wp|Mersenne twister}} table to get a 32-bit random number, discards the lowest 16 bits, and then discards the highest two bits (a bitwise ''and'' with 0x3FFF). If this number is 0, the game will choose a Pokémon in the party to be infected.


===In Generation III===
To determine what party member is to be infected, the game takes another value from the Mersenne twister table, multiplies it by the party count, then discards the lowest 32 bits of the result. If this number is an Egg, the calculation is repeated. Otherwise, if that party member has already been infected, nothing else will happen.
The Pokérus operates in much the same way as in Generation II, though it can infect {{pkmn|Egg}}s too. Also, it can only be contracted or cured in {{3v2|Ruby|Sapphire|Emerald}}. In {{2v2|FireRed|LeafGreen}}, as well as {{pkmn|Colosseum}} and {{Pokémon XD}}, since the [[time]] function is absent, and a Pokémon with Pokérus will keep it indefinitely (it can't spread Pokérus, either)<!-- at least FRLG!-->, until it is transferred to the [[Hoenn]]-based games.


====Nurse's comments====
If a Pokémon will be infected, the game takes the next value from the Mersenne twister table and discards the lowest 24 bits (if the lowest three bits of this result are all 0, another number is chosen). If any of the highest four bits are nonzero, the highest five bits are discarded. The resulting number will be '''X''', the Pokérus strain; the duration of the virus will be set to '''X''' modulo 4 + 1.
[[File:Pokerus screenshot RSE.png|thumb|right|240px|A player being told their Pokémon has caught Pokérus]]
"''Your <sc>Pokémon</sc> may be infected with <sc>Pokérus</sc>.<br>Little is known about the <sc>Pokérus</sc> except that they are microscopic life-forms that attach to <sc>Pokémon</sc>.<br>While infected, <sc>Pokémon</sc> are said to grow exceptionally well.''"


===In Generation IV===
These calculations mean that the strains 0 and 8 will never occur, and that the remaining strains are biased towards the lower numbers (with 1 through 7 being much more common than 9 through 15).
The mechanics remain the same from Generation III. Additionally, much like storage in {{g|Box Ruby & Sapphire}} and in the PC, storage in [[My Pokémon Ranch]] will keep a Pokémon's Pokérus status indefinitely.
 
{| class="roundy" style="text-align:center; border: 3px solid #A54ACE; background: #D67BFF"
! style="background: #EFA5EF" | X values
! style="background: #EFA5EF; {{roundytr|5px}}" | Chance to occur
|- style="background: #fff"
| 0, 8 || 0/224<br>(Cannot naturally occur)
|- style="background: #fff"
| 1, 2, 3, 4, 5, 6, 7 || 31/224<br>(13.83929%)
|-
| style="background: #fff; {{roundybl|5px}}" | 9, 10, 11, 12, 13, 14, 15
| style="background: #fff; {{roundybr|5px}}" | 1/224<br>(0.44643%)
|}


It will also double the effects of the new EV increasing items as well.
====Generation VI====
In Generation VI, the Pokérus does not affect EVs gained from [[Super Training]]. However, it increases the rate of [[Double-Up Bag]]s that are received during the training regimen. The icon that appears if a Pokémon has the Pokérus has been changed to spell out the full word, while the cured icon uses a design similar to the Gen V icon, with the mouth and eyes having a white color.


In {{2v2|HeartGold|SoulSilver}}, [[Professor Elm]] calls the player a little while after healing their first Pokémon with Pokérus and tells them that it has no effect and will wear off.
====Generation VII====
During battle, a Pokémon's summary will display a "Pokérus" icon beside its name if it has the Pokérus. The icon remains after the Pokémon is cured. An Egg infected with the Pokérus does not have this symbol on its summary screen. It can still spread the virus normally, and the Pokémon that hatches from the Egg will immediately acquire the icon.


If he is called back, he will claim that Pokémon will level up better with the Pokérus while infected.
Pokérus is not present in [[Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!]].


====Nurse's comments====
====Generation VIII====
"''Your Pokémon may be infected with the Pokérus.<br>Little is known about the Pokérus except that they are microscopic life-forms that attach to Pokémon.<br>While infected, Pokémon are said to grow exceptionally well.''"
In [[Sword and Shield]], a Pokémon's summary screen will show the Pokérus icon along with full text saying "POKÉRUS" with the typical smile icon next to the text. When cured, this text is then removed and only the cured icon is shown. These icons are shown with the rest of the Pokémon's icons such as the origin mark and shiny status. In the PC, this text is removed regardless if the Pokémon is infected or cured, only showing the face icon matching the status of infection. It can be seen next to the Pokémon's type and shiny status.


====Elm's explanation====
In [[Brilliant Diamond and Shining Pearl]], the Pokémon Center lady will tell the player that their Pokémon has been infected with Pokérus like in the original Diamond and Pearl games. The icon for the games is almost like how it was in Sword and Shield, except that the infected icon in the PC preview is contained in a pink box similar to how it is presented with text in the summary. The infection text in the Pokémon summary is written out as "Pokérus", with a capital P.
When calling the player: "''Hello, <player>?<br>I discovered an odd thing.<br>Apparently there's something called <sc>Pokérus</sc> that infects <sc>Pokémon</sc>.<br>Yes, it's like a virus, so it's called <sc>Pokérus</sc>.<br>It multiplies fast and infects other <sc>Pokémon</sc> too. But that's all.<br>It doesn't seem to do anything, and it goes away over time.<br>I guess it's nothing to worry about. Bye!''"


When called by the player: "''Hello, <player>?<br>It seems that <sc>Pokémon</sc> that have been infected with <sc>Pokérus</sc> level up better.<br>We're not quite sure why..."''
Pokérus does not appear natively in [[Pokémon Legends: Arceus]]. It cannot be contracted naturally, nor can infected Pokémon spread the virus to other party members. It also cannot progress towards becoming cured, and is not displayed on status screens. However, an infected Pokémon transferred into Legends: Arceus from Pokémon HOME will still gain bonus EVs during battle, despite no visible indicators of being infected, cured, or gaining EVs while it remains in Legends: Arceus.


===In Generation V===
====Generation IX====
The mechanics remain more or less the same, sharing similarity to the strain phenomenon in [[Generation II]]. However, a difference would be that the icon that would appear if a Pokémon has previously had Pokérus would be a pinkish color instead of the former yellow/orange color.
In {{g|Scarlet and Violet}}, Pokérus no longer generates naturally, does not spread to adjacent [[party]] Pokémon, cannot be seen on a Pokémon's [[summary]], and does not provide double [[effort values]] during battle. However, the data itself is retained in the data structure of the Pokémon, and will remain stored with the Pokémon if [[transfer]]red from previous games via [[Pokémon HOME]] into Scarlet or Violet, despite no longer having any visible indicator nor in-game effects.


To determine if any Pokémon in the player's party is to be infected, the game calls the Mersenne Twister table and then discards the lower half (16 bits) of the 32 bit number, then does & 0x3FFF (bitwise and) on the result. If the result is 0, a Pokémon in the party will be infected.
===Comments===
====Generation II====
To determine what party member is to be infected, the game takes another value from the Mersenne Twister table, multiplies it by the party count, then discards the lowest 32 bits of the result. If that party member already has been infected, nothing else will happen.
=====Pokémon Center lady's comments=====
"''Your {{ScPkmn}} appear to have tiny life forms stuck to them. <br> Your {{ScPkmn}} are healthy and seem to be fine. <br> But we can't tell you anything more at a <sc>Pokémon Center</sc>.''"


Now that the given Pokémon is to be infected, the game takes the next value from the Mersenne Twister table, discards the lower 24 bits, then enters a loop to determine the strain. The strains are biased towards the lower number strains. Once a strain has been determined, the duration the infection will last is determined. For a given strain ''s'', the duration is ''s''+''s''%4.
=====Elm's explanation=====
''"Hello, <player>? <br>I discovered an odd thing. <br>Apparently there's something called <sc>Pokérus</sc> that infects {{ScPkmn}}. <br>Yes, it's like a virus, so it's called <sc>Pokérus</sc>. <br>It multiplies fast and infects other {{ScPkmn}} too. But that's all. <br>It doesn't seem to do anything, and it goes away over time. <br>I guess it's nothing to worry about. Bye!"''


Refer to the Generation II table for strains and duration, as it is exactly the same. However, strains 0x0 and 0x8 are not obtainable legitimately.
====Generation III====
[[File:Pokerus screenshot RSE.png|thumb|right|240px|A player being told their Pokémon has caught the Pokérus]]
"''Your {{ScPkmn}} may be infected with <sc>Pokérus</sc>. <br>Little is known about the <sc>Pokérus</sc> except that they are microscopic life-forms that attach to {{ScPkmn}}. <br>While infected, {{ScPkmn}} are said to grow exceptionally well.''"


====Nurse's comments====
====Generation IV====
"''Oh... It looks like your Pokémon may be infected with the Pokérus. <br>Little is known about the Pokérus, except that it is a microscopic life-form that attaches to Pokémon. <br>While infected, Pokémon are said to grow exceptionally well.''"
=====Pokémon Center lady's comments=====
"''Your Pokémon may be infected with the Pokérus. <br>Little is known about the Pokérus except that they are microscopic life-forms that attach to Pokémon. <br>While infected, Pokémon are said to grow exceptionally well.''"


=====Elm's explanation=====
When calling the player: "''Hello, <player>? <br>I discovered an odd thing. <br>Apparently there's something called <sc>Pokérus</sc> that infects {{ScPkmn}}. <br>Yes, it's like a virus, so it's called <sc>Pokérus</sc>. <br>It multiplies fast and infects other {{ScPkmn}} too. But that's all. <br>It doesn't seem to do anything, and it goes away over time. <br>I guess it's nothing to worry about. Bye!''"


===In Generation VI===
When called by the player: "''Hello, <player>? <br>It seems that {{ScPkmn}} that have been infected with <sc>Pokérus</sc> level up better. <br>We're not quite sure why..."''
In Generation VI, Pokérus does not affect effort values gained during [[Super Training]].


====Nurse's comments====
====Generations V-VIII====
"''Oh... It looks like your Pokémon may be infected with the Pokérus. <br>Little is known about the Pokérus, except that it is a microscopic life-form that attaches to Pokémon. <br>While infected, Pokémon are said to grow exceptionally well.''"
"''Oh... It looks like your Pokémon may be infected with the Pokérus. <br>Little is known about the Pokérus, except that it is a microscopic life-form that attaches to Pokémon. <br>While infected, Pokémon are said to grow exceptionally well.''"


==Status icons==
==Status icons==
{| style="margin:auto; text-align:center; {{roundy|5px}} border: 2px solid #A54ACE; background: #D67BFF;"
{{incomplete|section|needs=XD active and cured}}
|-
<!--- Because of how G2 works, there is no icon for Pokérus active, but there is an "icon" for Pokérus cured --->
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px; height:60px"| [[Image:PokérusIC III.png]]
{| class="roundy" style="margin:auto; text-align:center; border: 2px solid #A54ACE; background: #D67BFF"
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px; height:60px"| [[Image:PokérusIC.png]]
|-
|- style="font-size: 80%;"
| style="{{roundy|60px}}|
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; height:60px" | [[File:PokérusIC Stad 2.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF" | [[File:PokérusIC III.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF" | [[File:PokérusIC Colo.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF" colspan="2" | [[File:PokérusIC IV V.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF" | [[File:PokérusIC VI.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF" | [[File:PokérusIC VII.png]]
| colspan="2" style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF" | [[File:PokérusIC VIII.png|x22px]]
|- style="font-size: 80%; white-space: nowrap"
|
| Icon from <br>{{color2|000|Pokémon Stadium 2|Stadium 2}}
| Icon from <br>{{color2|000|Generation III}}
| Icon from <br>{{color2|000|Generation III}}
| Icon from <br>{{color2|000|Generation IV|Generations IV}} and {{color2|000|Generation V|V}}
| Icon from <br>{{color2|000|Pokémon Colosseum|Colosseum}}
| colspan="2" | Icon from <br>{{color2|000|Generation IV|Generations IV}} and {{color2|000|Generation V|V}}
| Icon from <br>{{color2|000|Generation VI}}
| Icon from <br>{{color2|000|Generation VII}}
| colspan="2" | Icon from {{color2|000|Generation VIII}}
|-
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px; height:60px" | [[File:PokérusIC II cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC Stad 2 cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC III cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC Colo cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC IV cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC V cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC VI cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC VII cured.png]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC VIII infected.png|21px]]
| style="{{roundy|60px}} border: 2px solid #A54ACE; background: #EFA5EF; width:60px" | [[File:PokérusIC VIII cured.png|21px]]
|- style="font-size: 80%; white-space: nowrap"
| Cured icon from <br>{{color2|000|Generation II}}
| Cured icon from <br>{{color2|000|Pokémon Stadium 2|Stadium 2}}
| Cured icon from <br>{{color2|000|Generation III}}
| Cured icon from <br>{{color2|000|Pokémon Colosseum|Colosseum}}
| Cured icon from <br>{{color2|000|Generation IV}}
| Cured icon from <br>{{color2|000|Generation V}}
| Cured icon from <br>{{color2|000|Generation VI|Generation VI}}
| Cured icon from <br>{{color2|000|Generation VII|Generation VII}}
| colspan="2" | Infected and cured icons<br>from {{color2|000|Generation VIII|Generation VIII}} & {{color2|000|Pokémon HOME|Pokémon HOME}}
|}
|}


==In the anime==
==In the anime==
In ''[[SS008|Oaknapped]]'', [[Dr. Namba]] explained to {{an|Professor Oak}} that the mysterious viral lifeform Pokérus is an important component of the Pokémon Power Acceleration Project (PPAP), a secret project that aims to infect Pokémon with Pokérus to evolve them at a faster rate. However, all of his specimens have died out. Professor Oak also explains that the term "Pokérus" was coined by combining the words "Pokémon" and "virus" together. Later, Professor Oak began researching about the Pokérus and [[Team Rocket]]'s true intentions of using it.
In ''[[HS08|Oaknapped!]]'', [[Dr. Namba]] explained to {{an|Professor Oak}} that the mysterious viral lifeform Pokérus is an important component of his Pokémon Power Acceleration Project (PPAP), a secret project that aims to infect Pokémon with the Pokérus to [[Evolution|evolve]] them at a faster rate. However, all of his specimens had died out. Professor Oak also explains that the term "Pokérus" was coined by combining the words "Pokémon" and "virus" together. Later, Professor Oak began researching about the Pokérus and [[Team Rocket]]'s true intentions of using it.


==In the manga==
==In the manga==
===In the Pokémon Adventures manga===
===Pokémon Adventures===
Pokérus was discussed in ''[[PS439|Alternate Dimension Showdown IX]]'', when {{adv|Platinum}}'s team was discovered to have this virus and, as a result, became stronger. Her {{p|Froslass}}, {{p|Pachirisu}}, and {{p|Cherrim}} had it prior to being taken from the hospital, and then it spread to the rest of her party. At the hospital, [[Daisy Oak]] and [[Pokémon Professor#In the Pokémon Adventures manga|Yanase Berlitz]] realize the infection is, in fact, Pokérus.
===={{MangaArc|Platinum}}====
The Pokérus was discussed in ''[[PS439|The Final Dimensional Duel IX]]'', when {{adv|Platinum}}'s team was discovered to have this virus and, as a result, became stronger. Her {{TP|Platinum|Froslass}}, {{p|Pachirisu}}, and {{p|Cherrim}} had it prior to being taken from the hospital, and then it spread to the rest of her party. At the hospital, [[Daisy Oak]] and {{prof|Yanase Berlitz}} realize that the infection is, in fact, the Pokérus.


==Trivia==
==Trivia==
* Pokérus is an example of a mutualistic virus (while seemingly oxymoronic, a "virus" is classified by infecting cells, rather than negative effects), in which both host and virus benefit. Viruses with possible positive effects exist in the real world,<ref>http://www.nature.com/nature/journal/v447/n7142/full/nature05762.html</ref> but all of Pokérus's known effects are objectively positive. A notable difference between biological viruses and the Pokérus is that biological viruses infect a host cell by mutating the cell's DNA. Pokérus only affects the host Pokémon's [[effort values]], not the host's [[individual values]], which are regarded as the Pokémon analogue to DNA.
* The Pokérus is an example of a {{wp|Mutualism (biology)|mutualistic}} {{wp|virus}}, in which both host and virus benefit.
* The chance of encountering a [[Shiny Pokémon]] with Pokérus is 1/178,956,971. By comparison, the chance of getting struck by lightning is roughly 1/500,000, which means any given player is several hundred times more likely to get struck by lightning then to even encounter a Shiny pokemon with the Pokérus.
 
==In other languages==
{{langtable|color=EFA5EF|bordercolor=A54ACE
|zh_yue=寶可病毒 ''{{tt|Poké Behngduhk|Poké Virus}}''
|zh_cmn=寶可病毒 / 宝可病毒 ''{{tt|Poké Bìngdú|Poké Virus}}'' {{tt|*|Games}}<br>神奇寶貝病毒 ''{{tt|Shénqí Bǎobèi Bìngdú|Pokémon Virus}}'' {{tt|*|Manga}}
|fr=Pokérus
|de=Pokérus
|it=Pokérus
|ko=포켓러스 ''Pokérus''
|es=Pokérus
|vi=Pokévirus
|pt=Pokérus
}}


==References==
==References==
<references/>
{{reflist}}
 
{{-}}
{{Project Games notice|game mechanic}}
{{Project Games notice|game mechanic}}


[[Category:Game mechanics]]
[[Category:Game mechanics]]


[[de:PokéRus]]
[[de:Pokérus]]
[[es:Pokérus]]
[[es:Pokérus]]
[[fr:Pokérus]]
[[fr:Pokérus]]
[[it:Pokérus]]
[[it:Pokérus]]
[[ja:ポケルス]]
[[ja:ポケルス]]
[[zh:神奇寶貝病毒]]
[[zh:寶可病毒]]

Latest revision as of 10:10, 9 August 2024

013Weedle.png Pokérus is in need of spading. See its section on the spading page for more information, and how you can help.
Pokémon infected with Pokérus in Pokémon Adventures

The Pokérus (Japanese: ポケルス Pokérus), from "Pokémon virus", is a microscopic life-form that may attach to Pokémon, first appearing in the Generation II games. It is a beneficial mechanic that a Pokémon can obtain.

In the games

When a Pokémon has the Pokérus, it gains double the effort values from battling (e.g., fighting a Magikarp will give two Speed EVs, rather than one). Effort points gained from Vitamins and Feathers are not doubled. The infected Pokémon can infect other Pokémon with the virus for a period of one to four days. However, the Pokérus timer can be delayed by several methods, such as by placing the infected Pokémon in a PC Box.

While it is represented similarly to status conditions, the Pokérus is not a status condition, so it cannot be healed at a Pokémon Center or with any status condition healing item.

Pokérus has a 3 in 65,536 (or approximately a 1 in 21,845) chance of being generated on one of the player's Pokémon after a battle, making it rarer than encountering or hatching a Shiny Pokémon. If any of the player's Pokémon are infected, the Pokérus may spread among Pokémon in the player's party after any battle.

From Generation IV onward, the Pokérus became more accessible, with worldwide trading facilitated by Nintendo Wi-Fi Connection.

Infection

When a Pokémon is infected with the Pokérus, their status screen will display an icon indicating this special "status" the same way status conditions would be noted. If the Pokémon becomes affected by a status condition such as Sleep, the Pokérus icon will be temporarily replaced until the status condition is cured. As long as the Pokémon is infected with the Pokérus, it can spread the virus to other Pokémon in the player's party.

The Pokérus may spread if an infected Pokémon is in the player's party after a battle. The Pokérus may only spread to a Pokémon directly adjacent to an already infected Pokémon, and only if they have never had Pokérus before. Eggs may catch the Pokérus like any other Pokémon.

Becoming cured

A Pokérus infection only progresses towards cured status when a new day starts with the infected Pokémon in the party (or if, when the game is loaded, it is not the same day as it was when the game was saved). The number of days before a Pokémon will be cured of the Pokérus can vary from one to four days. Once this time has passed, the Pokémon becomes cured and will be immune to the virus in the future. The Pokémon still gains double effort values when cured.

Due to the beneficial nature of the Pokérus, players will often place an infected Pokémon in the PC where it will keep the infection indefinitely, so that it may be withdrawn to spread the virus at will. Other options include putting a Pokémon in the Day Care or sending it to Stadium 2 in Generation II, Pokémon Box Ruby & Sapphire in Generation III, My Pokémon Ranch in Generation IV, Pokémon Bank in Generation VI and Generation VII, or Pokémon HOME in Generation VIII.

In Generation III, if the player deposits an infected Pokémon inside a PC, saves inside a Pokémon Center prior to midnight, shuts off the game, resumes the game after midnight, withdraws the infected Pokémon from the PC, and exits the Pokémon Center, it is possible for the infected Pokémon to be cured of the Pokérus upon stepping outside of the building. This does not happen in any other generation.

In Generation VIII, the game will check on the next available random event increment after midnight. This can result in a Pokémon that was infected while in a box, and withdrawn directly after resuming the game from sleep, being subsequently cured of the Pokérus after the next battle or similar event.

Technical information

The Pokérus is stored in a Pokémon's data structure as a single byte. In hexadecimal, this can be represented as a two-digit number XY. The upper 4 bits of the byte, X, represent the specific strain of the Pokérus the Pokémon has contracted. The lower 4 bits, Y, represent the number of days remaining before the infected Pokémon is cured of the virus.

A Pokémon is or has been infected if X (the strain) is a nonzero value. If Y (days remaining) is nonzero when X is also nonzero, this means the Pokémon is currently infected. If Y is 0 and X is nonzero, then the Pokémon is "cured" of the Pokérus. If both X and Y are 0, then the Pokémon has never been affected by the Pokérus.

Whenever the game's internal clock strikes midnight, every currently infected Pokémon in the player's party has their Pokérus value decreased by one. Once the Y value reaches 0, the Pokémon will be cured of the Pokérus.

Strains

Whenever the game creates the Pokérus on a Pokémon, the value assigned to Y (days) depends on the value assigned to X (strain). Specifically, the number of days will be set to X modulo 4 + 1. In other words, the higher two bits of X are irrelevant to the "strain".

Strain X values Duration
(Y value)
A 0, 4, 8, 12 1 day
B 1, 5, 9, 13 2 days
C 2, 6, 10, 14 3 days
D 3, 7, 11, 15 4 days

Whenever the Pokérus spreads from an infected Pokémon to a new Pokémon, the new Pokémon inherits the infected Pokémon's strain of the Pokérus (X) and Y is copied directly from the infected Pokémon. As an example, if a Pokémon has the Pokérus with an X value of 7 and a Y value of 2 (2 days remaining before it will be cured) and it infects another Pokémon, the new Pokémon will be infected with Pokérus with an X value of 7 and a Y value of 2. Infecting other Pokémon does not reset the Y value to the default value for a given strain on the newly infected Pokémon, nor for the original host.

In Pokémon Emerald onward, X values of 0 and 8 do not generate legitimately, as the RNG doesn't permit these values to generate. Additionally with a value of 0, upon being "cured" the Pokémon would appear to have never had the Pokérus at all.

After having the virus

Once a Pokémon's immune system has fought off the virus, they cannot spread it further, nor can it be spread to them by other Pokémon. In Generations II and III, a dot will appear on the Pokémon's status screen to indicate that they have had the virus previously, while in Generation IV and onward, it will be a small face. Though the virus is gone, the Pokémon will still gain twice the EVs it would have gained before the virus.

Differences between generations

Generation II

When the player first encounters the virus in one of the Generation II games, the Pokémon Center lady at the Pokémon Center will make note of it when the Pokémon is first healed after contracting it, saying that there are "tiny life forms" on the Pokémon. After leaving the Pokémon Center, Professor Elm will call the player to tell them that the virus has no effect and will wear off. A Pokémon with active Pokérus will list its status as such, and a Pokémon that has had the Pokérus and is cured will have a small dot near its HP meter on the status screen. At the end of a battle, the virus has a 1/3 chance to spread. If the infected Pokémon is adjacent to two Pokémon who have never had it before, one of them will catch the Pokérus. Pokérus can infect Eggs as well. An indicator for Pokérus will not show up on the Egg's status screen, but once it hatches, it will appear under its status on the status screen like normal.

If a Pokémon with any stage of the Pokérus (active or cured) is traded back to a Generation I game, or withdrawn from Pokémon Stadium 2 by a Generation I game, all traces of that Pokémon having had the Pokérus will disappear. This is because a Pokémon's Pokérus status is not saved in any form in the Generation I games, thereby making it possible for a Pokémon to legitimately contract the Pokérus multiple times by trading it back and forth, once it becomes cured of a given infection. The only benefit of doing so would be to allow other Pokémon to contract the virus.

The Pokérus cannot randomly occur before the player has visited Goldenrod City[1] (but it may spread between Pokémon before then). If a Pokémon in the party has the Pokérus, other Pokémon cannot randomly contract it; they can only receive it from that Pokémon.[2]

Infection and spread details
050Diglett.png This section is incomplete.
Please feel free to edit this section to add missing information and complete it.
Reason: Description of the random byte generation algorithm, which is that used by other random byte-needing routines

The party is first iterated over to determine if any member has the Pokérus. If so, the spread code is called for each member with the Pokérus and not the new infection code, and if not vice versa.

The spread code checks if a random byte is less than 85 and if the party has multiple members before proceeding as follows: if the spreader is the last party member, or if a random byte is less than 128, iterate backwards, otherwise iterate forwards. If the member being iterated over has an active infection, they are skipped over and become the spreader. If they are clear and never had the Pokérus, they are infected. The Y value for an infection is generated from the X value as it is for a spontaneous infection, unlike in future games where it is copied. The iteration stops when a member is newly infected, when it reaches a cured member, or when it would be about to pass through the beginning or end of the party.

The new infection code first checks if the flag for having visited Goldenrod City is set, terminating if not. Then, it checks if a random byte is equal to zero and another random byte is less than three, terminating if not. It then chooses a random party member by generating a random byte and keeping its bottom three bits (bitwise and with seven), rerolling until that number is a valid party index. If that party member has ever had the Pokérus, the code terminates. Otherwise, a random byte is rolled, rerolling if zero until not zero. This byte shall be represented as AB (not to be confused with registers A and B) in the same way that the Pokérus byte is represented as XY. If A is not zero, B's bottom three bits (bitwise and with seven) are copied as a four-bit value, incremented, and put into X, and X's bottom two bits (bitwise and with three) are copied as a three-bit value, incremented, and put into Y. Otherwise, it is likely intended to copy B into X, but, perhaps due to a misplaced load, zero is copied into X instead; Y is then derived from X with the same code as with A not zero, but since X is always zero, Y is always one. (If the misplaced load is placed in a more logical place, the Y value ends up always being one anyway, so there may have been more required effort to make the code work as intended.)

X values of zero and eight can occur naturally: the latter is as designed, the former is due to the above bug. Due to this bug, an X value above eight cannot occur naturally. Probabilities of each strain is as follows:

X values Chance to occur
0 15/255
(5.88235%)
1, 2, 3, 4, 5, 6, 7, 8 30/255
(11.76471%)
9, 10, 11, 12, 13, 14, 15 0/255
(Cannot naturally occur)

Generation III

The Pokérus can only be contracted or cured in Ruby, Sapphire, and Emerald. In FireRed and LeafGreen, as well as Colosseum and Pokémon XD, since the time function is absent, a Pokémon with the Pokérus will keep it indefinitely (it can't spread the Pokérus, either), until it is transferred to the Hoenn-based games. When a Pokémon can spread the Pokérus, it has a 1/3 chance to spread it to both adjacent Pokémon.

Otherwise, the Pokérus operates in much the same way as in Generation II, but it is now possible for the Pokérus to be randomly contracted even when another Pokémon in the party already has it (and the Pokérus can spread after the same battle where it was contracted)[3], and there is no location requirement before the Pokérus can randomly be contracted. Eggs infected with Pokérus will now indicate as such.

In Ruby and Sapphire only[4], X values of 0 and 8 do occur naturally, whereas in Pokémon Emerald onward, the RNG does not allow them to occur at all. The following is the chance to obtain each strain in Ruby and Sapphire:

X values Chance to occur
0 30/255
(11.76470%)
1, 2, 3, 4, 5, 6, 7 31/255
(12.15686%)
8, 9, 10, 11, 12, 13, 14, 15 1/255
(0.39215%)

Generation IV

The mechanics remain the same from Generation III. Additionally, much like storage in Pokémon Box Ruby & Sapphire and in the PC, storage in My Pokémon Ranch will keep a Pokémon's Pokérus status indefinitely. The Pokérus doubles the EVs earned from Power items.

In HeartGold and SoulSilver, Professor Elm calls the player soon after healing their first Pokémon with the Pokérus to tell them that it has no effect and will wear off. If he is called back, he will claim that Pokémon will level up better with the Pokérus while infected.

Generation V

The mechanics remain more or less the same, but now the icon that appears if a Pokémon has previously had the Pokérus is pinkish in color instead of the former yellow/orange color.

Pseudorandom number generation

To determine if any Pokémon in the player's party is to be infected, the game calls the Mersenne twister table to get a 32-bit random number, discards the lowest 16 bits, and then discards the highest two bits (a bitwise and with 0x3FFF). If this number is 0, the game will choose a Pokémon in the party to be infected.

To determine what party member is to be infected, the game takes another value from the Mersenne twister table, multiplies it by the party count, then discards the lowest 32 bits of the result. If this number is an Egg, the calculation is repeated. Otherwise, if that party member has already been infected, nothing else will happen.

If a Pokémon will be infected, the game takes the next value from the Mersenne twister table and discards the lowest 24 bits (if the lowest three bits of this result are all 0, another number is chosen). If any of the highest four bits are nonzero, the highest five bits are discarded. The resulting number will be X, the Pokérus strain; the duration of the virus will be set to X modulo 4 + 1.

These calculations mean that the strains 0 and 8 will never occur, and that the remaining strains are biased towards the lower numbers (with 1 through 7 being much more common than 9 through 15).

X values Chance to occur
0, 8 0/224
(Cannot naturally occur)
1, 2, 3, 4, 5, 6, 7 31/224
(13.83929%)
9, 10, 11, 12, 13, 14, 15 1/224
(0.44643%)

Generation VI

In Generation VI, the Pokérus does not affect EVs gained from Super Training. However, it increases the rate of Double-Up Bags that are received during the training regimen. The icon that appears if a Pokémon has the Pokérus has been changed to spell out the full word, while the cured icon uses a design similar to the Gen V icon, with the mouth and eyes having a white color.

Generation VII

During battle, a Pokémon's summary will display a "Pokérus" icon beside its name if it has the Pokérus. The icon remains after the Pokémon is cured. An Egg infected with the Pokérus does not have this symbol on its summary screen. It can still spread the virus normally, and the Pokémon that hatches from the Egg will immediately acquire the icon.

Pokérus is not present in Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!.

Generation VIII

In Sword and Shield, a Pokémon's summary screen will show the Pokérus icon along with full text saying "POKÉRUS" with the typical smile icon next to the text. When cured, this text is then removed and only the cured icon is shown. These icons are shown with the rest of the Pokémon's icons such as the origin mark and shiny status. In the PC, this text is removed regardless if the Pokémon is infected or cured, only showing the face icon matching the status of infection. It can be seen next to the Pokémon's type and shiny status.

In Brilliant Diamond and Shining Pearl, the Pokémon Center lady will tell the player that their Pokémon has been infected with Pokérus like in the original Diamond and Pearl games. The icon for the games is almost like how it was in Sword and Shield, except that the infected icon in the PC preview is contained in a pink box similar to how it is presented with text in the summary. The infection text in the Pokémon summary is written out as "Pokérus", with a capital P.

Pokérus does not appear natively in Pokémon Legends: Arceus. It cannot be contracted naturally, nor can infected Pokémon spread the virus to other party members. It also cannot progress towards becoming cured, and is not displayed on status screens. However, an infected Pokémon transferred into Legends: Arceus from Pokémon HOME will still gain bonus EVs during battle, despite no visible indicators of being infected, cured, or gaining EVs while it remains in Legends: Arceus.

Generation IX

In Pokémon Scarlet and Violet, Pokérus no longer generates naturally, does not spread to adjacent party Pokémon, cannot be seen on a Pokémon's summary, and does not provide double effort values during battle. However, the data itself is retained in the data structure of the Pokémon, and will remain stored with the Pokémon if transferred from previous games via Pokémon HOME into Scarlet or Violet, despite no longer having any visible indicator nor in-game effects.

Comments

Generation II

Pokémon Center lady's comments

"Your Pokémon appear to have tiny life forms stuck to them.
Your Pokémon are healthy and seem to be fine.
But we can't tell you anything more at a Pokémon Center."

Elm's explanation

"Hello, <player>?
I discovered an odd thing.
Apparently there's something called Pokérus that infects Pokémon.
Yes, it's like a virus, so it's called Pokérus.
It multiplies fast and infects other Pokémon too. But that's all.
It doesn't seem to do anything, and it goes away over time.
I guess it's nothing to worry about. Bye!"

Generation III

A player being told their Pokémon has caught the Pokérus

"Your Pokémon may be infected with Pokérus.
Little is known about the Pokérus except that they are microscopic life-forms that attach to Pokémon.
While infected, Pokémon are said to grow exceptionally well."

Generation IV

Pokémon Center lady's comments

"Your Pokémon may be infected with the Pokérus.
Little is known about the Pokérus except that they are microscopic life-forms that attach to Pokémon.
While infected, Pokémon are said to grow exceptionally well."

Elm's explanation

When calling the player: "Hello, <player>?
I discovered an odd thing.
Apparently there's something called Pokérus that infects Pokémon.
Yes, it's like a virus, so it's called Pokérus.
It multiplies fast and infects other Pokémon too. But that's all.
It doesn't seem to do anything, and it goes away over time.
I guess it's nothing to worry about. Bye!"

When called by the player: "Hello, <player>?
It seems that Pokémon that have been infected with Pokérus level up better.
We're not quite sure why..."

Generations V-VIII

"Oh... It looks like your Pokémon may be infected with the Pokérus.
Little is known about the Pokérus, except that it is a microscopic life-form that attaches to Pokémon.
While infected, Pokémon are said to grow exceptionally well."

Status icons

050Diglett.png This section is incomplete.
Please feel free to edit this section to add missing information and complete it.
Reason: XD active and cured
PokérusIC Stad 2.png PokérusIC III.png PokérusIC Colo.png PokérusIC IV V.png PokérusIC VI.png PokérusIC VII.png PokérusIC VIII.png
Icon from
Stadium 2 		Icon from
Generation III 		Icon from
Colosseum 		Icon from
Generations IV and V 		Icon from
Generation VI 		Icon from
Generation VII 		Icon from Generation VIII
PokérusIC II cured.png PokérusIC Stad 2 cured.png PokérusIC III cured.png PokérusIC Colo cured.png PokérusIC IV cured.png PokérusIC V cured.png PokérusIC VI cured.png PokérusIC VII cured.png PokérusIC VIII infected.png PokérusIC VIII cured.png
Cured icon from
Generation II 		Cured icon from
Stadium 2 		Cured icon from
Generation III 		Cured icon from
Colosseum 		Cured icon from
Generation IV 		Cured icon from
Generation V 		Cured icon from
Generation VI 		Cured icon from
Generation VII 		Infected and cured icons
from Generation VIII & Pokémon HOME

In the anime

In Oaknapped!, Dr. Namba explained to Professor Oak that the mysterious viral lifeform Pokérus is an important component of his Pokémon Power Acceleration Project (PPAP), a secret project that aims to infect Pokémon with the Pokérus to evolve them at a faster rate. However, all of his specimens had died out. Professor Oak also explains that the term "Pokérus" was coined by combining the words "Pokémon" and "virus" together. Later, Professor Oak began researching about the Pokérus and Team Rocket's true intentions of using it.

In the manga

Pokémon Adventures

Platinum arc

The Pokérus was discussed in The Final Dimensional Duel IX, when Platinum's team was discovered to have this virus and, as a result, became stronger. Her Froslass, Pachirisu, and Cherrim had it prior to being taken from the hospital, and then it spread to the rest of her party. At the hospital, Daisy Oak and Yanase Berlitz realize that the infection is, in fact, the Pokérus.

Trivia

  • The Pokérus is an example of a mutualistic virus, in which both host and virus benefit.

In other languages

Language Title
Chinese Cantonese 寶可病毒 Poké Behngduhk
Mandarin 寶可病毒 / 宝可病毒 Poké Bìngdú *
神奇寶貝病毒 Shénqí Bǎobèi Bìngdú *
France Flag.png French Pokérus
Germany Flag.png German Pokérus
Italy Flag.png Italian Pokérus
South Korea Flag.png Korean 포켓러스 Pokérus
Portugal Flag.png Portuguese Pokérus
Spain Flag.png Spanish Pokérus
Vietnam Flag.png Vietnamese Pokévirus

References

  1. ↑ pret/pokegold: pokerus.asm lines 19-20
  2. ↑ pret/pokegold: pokerus.asm lines 7-10
  3. ↑ pret/pokeruby: battle_main.c lines 5125-5129
  4. ↑ Pokerus Logic in Ruby Disassembly


Project Games logo.png This game mechanic article is part of Project Games, a Bulbapedia project that aims to write comprehensive articles on the Pokémon games.
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