Methods of Evolution
There are numerous methods of evolution which define how and when Pokémon evolve. Most Pokémon will evolve by leveling up while others evolve through specific means, such as being traded, achieving a certain amount of friendship or leveling at certain times, among others.
Triggers
Across all generations, Pokémon may only evolve after one of three events:
Though these three are the activating events for evolution, there is always a catalyst required for the evolution to begin. If the catalyst is present and the evolutionary event is activated, the Pokémon will evolve at the end of the process that caused the activating event (at the end of a battle or after a trade has been completed). An Everstone held by the Pokémon will always prevent the evolution by level up or trade, but not by exposure to an evolutionary stone (except the evolution of Kadabra to Alakazam via trade in Generation IV and V, due to a glitch).
Leveling up
Most Pokémon that evolve do so after leveling up. This can be triggered by gaining experience in battle or by using a Rare Candy. Sometimes, several additional conditions must be met in addition to gaining a level for a Pokémon to evolve, such as being at or above a specific level, knowing a move, or being in a specific place. When these conditions are met, a Pokémon will attempt to evolve every time it gains a level unless the conditions are removed. A Pokémon left in the Day Care will not evolve, though, even if the conditions are met. Pokémon will also not evolve if player loses the battle, no matter if the conditions are met.
Note that if a Pokémon levels up under the conditions required for evolution and then faints before the battle is over, the Pokémon will still attempt to evolve at the end of the battle, but will not be revived from fainting.
| Leveling up | ||
|---|---|---|
 Chikorita |
→ Level up |
 Bayleef |
At or above a certain level
- Main article: List of Pokémon that evolve at or above a certain level
Most Pokémon, with at least one in nearly every evolution family, will evolve when they reach or surpass a certain level. A Pokémon that levels up to this level or a higher level will attempt to evolve every time it does so, at the end of the battle in which it attained this level or after a Rare Candy has been used.
When friendship is high
- See also: Pokémon that evolve by friendship
Some Pokémon will only evolve when their friendship reaches 220 or above and they are leveled up. This is most common with baby Pokémon; however, some others also evolve in this way. Like the friendship system itself, this method of evolution first debuted in Generation II. Like those which evolve when at or above a certain level, a happy Pokémon will attempt to evolve every level until it hits level 100, unless its friendship is reduced.
Although Pichu evolves when its friendship is high, the Spiky-eared Pichu in Pokémon HeartGold and SoulSilver is an exception and will never evolve.
| Friendship | ||
|---|---|---|
 Togepi |
→ Friendship |
 Togetic |
When the Pokémon knows a certain move
- See also: Pokémon that evolve with certain moves
Some Pokémon evolve only if they currently know a certain move and are then leveled up. These moves are commonly available by leveling up (in which case the Pokémon will evolve at the end of the battle in which it learned the move), though some must be taught via Move Reminder. This method was introduced in Generation IV.
| Knowing a move | ||
|---|---|---|
 Piloswine |
→ Level up knowing AncientPower |
 Mamoswine |
When trained in a certain area
Some Pokémon can evolve if they gain a level while training in a certain location. Several evolutions introduced in Generation IV take advantage of this. So far, this method has only been possible in the Sinnoh and Unova regions.
| In a certain location | ||
|---|---|---|
 Nosepass |
→ Level up in Mt. Coronet or Chargestone Cave |
 Probopass |
When holding an item
Several Pokémon evolve if they level up while holding a specific evolution-inducing held item. When this occurs, the item disappears upon completion of the evolution. Currently, every Pokémon who evolves in this way must also level up at a certain time.
| Holding an item | ||
|---|---|---|
 Sneasel |
→ Level up holding Razor Claw (Night) |
 Weavile |
At certain times
- See also: Pokémon that evolve based on time
The current time will sometimes affect evolution, but it is never the sole catalyst; it always is used in tandem with another (currently, friendship and a held item are the only methods it is paired with).
| At certain times | ||
|---|---|---|
 Gligar |
→ Level up holding Razor Fang (Night) |
 Gliscor |
Unique conditions
The following Pokémon evolve through a method that is isolated to their evolution line only.
- Eevee evolves into Espeon when it levels up if the Sun Shard is in the Bag, or into Umbreon when it levels up if the Moon Shard is in the Bag. These key items only exist in Pokémon XD: Gale of Darkness, and only one of the two can be obtained.
- Mantyke evolves into Mantine when it levels up if there is a Remoraid in the user's party.
- Feebas evolves into Milotic when it levels up if its Beauty condition is 170 or above.
- Combee evolves into a Vespiquen at level 21 if it is female. Male Combee do not evolve.
- When Nincada evolves into Ninjask at level 20, if there is an empty slot in the party, a Shedinja will appear. From Generation IV onward, the player must also have a spare standard Poké Ball in their Bag.
Additional factors
Some Pokémon from branched evolution families evolve into different forms depending on some additional factors. These factors are not conditions for evolution, since they do not determine the possibility of evolution, but what the Pokémon will become after evolution.
- Burmy evolves at level 20, but its new form is determined by its gender and, if female, its cloak (which changes according to the place where it has battled last time).
- Tyrogue evolves at level 20, depending on its stats.
- Hitmonlee if Attack > Defense
- Hitmonchan if Attack < Defense
- Hitmontop if Attack = Defense
- Wurmple evolves at level 7 into Silcoon or Cascoon, depending on its personality value. It is a hidden value determined when Pokémon is caught and cannot be affected by the player.
Evolving by evolutionary stone
- Main article: Evolutionary stone
- See also: Pokémon that evolve by evolutionary stone
Some Pokémon evolve when they are exposed to an evolutionary stone. The stone may be applied at any time and causes an instant evolution. The player can decide whether and when to evolve his or her Pokémon, but he or she must choose carefully as most Pokémon will no longer be able to learn certain moves when they evolve in this way, and some (like Raichu and Togekiss) cannot learn any moves by leveling up, although there are exceptions to this rule and certain moves are exclusive to the stone-evolved Pokémon.
The starter Pikachu on Pokémon Yellow (or any Pikachu with the same OT and ID number) will refuse to take the Thunderstone.
| Using a stone | ||
|---|---|---|
 Growlithe |
→ Fire Stone |
 Arcanine |
Usually there are no special requirements for stone-induced evolution, with only two exceptions: Kirlia and Snorunt.
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Note that sometimes the Oval Stone is said to be an evolutionary stone, because it is a stone and it is required for an evolution. However, technically Oval Stone is an evolution-inducing held item, which Happiny must be holding to evolve into Chansey when it levels up.
Evolution via trading
- Main article: Trade
- See also: Pokémon that evolve through trading
A few Pokémon evolve only when they are traded. The evolution starts immediately after the trade is completed, regardless of the method of trading used. However, sometimes there are additional conditions.
| Trade | ||
|---|---|---|
 Haunter |
→ Trade |
 Gengar |
Holding a certain item
- Main article: Evolution-inducing held item
- See also: Pokémon that evolve by trading with a held item
Some Pokémon evolve when traded only if they are holding a certain item. Like any evolution-inducing held item, the item disappears after the Pokémon evolves.
| Trade while holding an item | ||
|---|---|---|
 Electabuzz |
→ Trade Holding an Electirizer |
 Electivire |
Trading for a certain Pokémon
Some Pokémon evolve when traded with a specific Pokémon. Only two Pokémon do this so far and evolve each other through this method.
| Trade for certain Pokémon | ||
|---|---|---|
 Shelmet |
→ Trade For a Karrablast |
 Accelgor |
 Karrablast |
→ Trade For a Shelmet |
 Escavalier |
