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[[File:Key System menu.png|frame|The Key System menu]]
The '''Key System''' (Japanese: '''キーシステム''' ''Key System'') is a feature of the [[Unova Link]] in [[Pokémon Black and White Versions 2|Pokémon Black 2 and White 2]]. It allows players to change the difficulty level of the game, switch between [[Black City]] and [[White Forest]], and change the Mystery Door in the [[Underground Ruins]]. They can be shared between players using the Unova Link, but players can only share the keys that are exclusive to their version.

==Difficulty==
There are three different difficulties: '''Easy Mode''' (Japanese: '''アシストモード''' ''Assist Mode''), '''Normal Mode''' (Japanese: '''ノーマルモード''' ''Normal Mode''), and '''Challenge Mode''' (Japanese: '''チャレンジモード''' ''Challenge Mode''). Only Normal Mode is unlocked by default; Easy Mode and Challenge Mode are exclusive to White 2 and Black 2 respectively, and are unlocked by defeating the Champion. This awards the player with the '''Easy Key''' (Japanese: '''アシストキー''' ''Assist Key'') in White 2 or the '''Challenge Key''' (Japanese: '''チャレンジキー''' ''Challenge Key'') in Black 2.

Because keys are tied to the save file, starting a new game or deleting the save file will also remove any unlocked keys. Therefore, the only way to play the main storyline with a difficulty other than Normal Mode is to transfer another player's key from a separate DS/3DS system.

In Easy Mode, opponents use less competent {{wp|artificial intelligence}} and the [[level]] of opposing Trainers' Pokémon are lower than usual. However, their Pokémon's stats are still calculated using the levels from Normal Mode (for example, Champion [[Iris]]'s {{p|Haxorus}} will appear to be level 55 but still have the stats of a level 59 Haxorus). The lowered levels are taken into account for [[prize money]] (the player will receive less), but not [[experience]] (in the example, the player's Pokémon will still receive experience as if they had defeated a level 59 Haxorus).

In Challenge Mode, opponents use more competent {{wp|artificial intelligence}} and the [[level]] of opposing Trainers' Pokémon are higher than usual (1 level higher at the start of the game, and rising to 5 levels higher by the end of the game). [[Gym Leader]]s and the [[Elite Four]] each use one additional Pokémon on their team, as well as their party having different [[move]]sets and [[held item]]s, and their Pokémon's {{IV}}s are all set to 30. However, Trainers' Pokémon's stats are still calculated using the levels from Normal Mode (for example, Champion Iris's Haxorus will appear to be level 63 but still have the stats of a level 59 Haxorus). The raised levels are taken into account for both prize money and experience (the player and their Pokémon will receive more of each).

==City==
The version exclusive cities, [[Black City]] and [[White Forest]], are found by default in Black Version 2 and White Version 2, respectively. They can be unlocked in the opposite game if certain conditions are met.

After completing five areas of [[Black Tower]] in Black 2, the player will be rewarded with the '''Tower Key''' (Japanese: '''まてんろうのカギ''' ''Skyscraper Key''). This can be transferred to White 2, which will unlock access to Black City. Likewise, after White 2 players have completed five areas of [[White Treehollow]], the '''Treehollow Key''' (Japanese: '''じゅどうのカギ''' ''Tree Hollow Key'') can be transferred to Black 2. This unlocks White Forest for Black 2 players.

Players of either version can use the [[Unova Link]] to switch between cities once both are unlocked. However, the cities cannot be switched if the player had saved their game within the current city.

==Mystery Door==
A mysterious door in the [[Clay Tunnel]] gives access to the [[Underground Ruins]], where the [[legendary giants]] can be found, though only one giant will appear at a time, depending on which key is active. {{p|Regirock}} is the default Pokémon in both Black 2 and White 2. Upon catching Regirock (and not just defeating it, fleeing from it or obtaining it from another game), Black 2 players are rewarded with the '''Iron Key''' (Japanese: '''くろがねのカギ''' ''Iron Key'') and White 2 players with the '''Iceberg Key''' (Japanese: '''ひょうざんのカギ''' ''Iceberg Key''); these allow access to {{p|Registeel}} and {{p|Regice}}, respectively. Players can obtain their final key by transferring it from the opposite version through Unova Link.

==Trivia==
* It is possible to receive a transferred key on a game that does not have a save file yet. If the player then starts a new game, they will keep the key. If the player then quits the new game without ever saving and starts another new game, they will still keep the key. However, if the player saves, then either removing the save file or starting a new game will remove the key.<ref>https://www.youtube.com/watch?v=m5B_2AT2G7w</ref>

==In other languages==
{{langtable|color={{black 2 color}}|bordercolor={{white 2 color}}|textcolor=FFF
|da=Nøglesystemet
|fr=Trousseau
|de=Schlüsselsystem
|it=Sistema a chiave
|ko=키 시스템 ''Key System''
|es=Sistema Clave
|sv=Nyckelsystemet
}}
<div style="display:inline-block">
''Easy Mode''
{{langtable|color={{white 2 color light}}|bordercolor={{white 2 color}}
|fr=Mode assisté
|de=Hilfsmodus
|it=Modalità aiuto
|ko=어시스트 모드 ''Assist Mode''
|es=Modo Ayuda
}}</div>
<div style="display:inline-block">
''Normal Mode''
{{langtable|color={{black 2 color}}|bordercolor={{white 2 color}}|textcolor=FFF
|fr=Mode normal
|de=Standardmodus
|it=Modalità normale
|ko=노말모드 ''Normal Mode''
|es=Modo Normal
}}</div>
<div style="display:inline-block">
''Challenge Mode''
{{langtable|color={{black 2 color light}}|bordercolor={{black 2 color}}
|fr=Mode challenge
|de=Hürdenmodus
|it=Modalità ostacolo
|ko=챌린지 모드 ''Challenge Mode''
|es=Modo Reto
}}</div>
<div style="display:inline-block">
''Easy Key''
{{langtable|color={{white 2 color light}}|bordercolor={{white 2 color}}
|fr=Clé Assistance
|de=Hilfsschlüssel
|it=Chiave aiuto
|ko=어시스트 키 ''Assist Key''
|es=Clave Ayuda
}}</div>
<div style="display:inline-block">
''Challenge Key''
{{langtable|color={{black 2 color light}}|bordercolor={{black 2 color}}
|fr=Clé Challenge
|de=Hürdenschlüssel
|it=Chiave ostacolo
|ko=챌린지 키 ''Challenge Key''
|es=Clave Reto
}}</div>
<div style="display:inline-block">
''Tower Key''
{{langtable|color={{black 2 color light}}|bordercolor={{black 2 color}}
|fr=Clé Gratte-Ciel
|de=S-Schlüssel
|it=Chiave grattacielo
|ko=마천루의 열쇠 ''Macheollu-ui Yeolsoe''
|es=Clave Rascacielos
}}</div>
<div style="display:inline-block">
''Treehollow Key''
{{langtable|color={{white 2 color light}}|bordercolor={{white 2 color}}
|fr=Clé Arbre Creux
|de=W-Schlüssel
|it=Chiave antro
|ko=수동의 열쇠 ''Sudong-ui Yeolsoe''
|es=Clave Cavernogal
}}</div>
<div style="display:inline-block">
''Iron Key''
{{langtable|color={{black 2 color light}}|bordercolor={{black 2 color}}
|fr=Clé Fer
|de=Eisenschlüssel
|it=Chiave ferro
|ko=쇠철의 열쇠 ''Soecheol-ui Yeolsoe''
|es=Clave Hierro
}}</div>
<div style="display:inline-block">
''Iceberg Key''
{{langtable|color={{white 2 color light}}|bordercolor={{white 2 color}}
|fr=Clé Iceberg
|de=Eisbergschlüssel
|it=Chiave iceberg
|ko=빙산의 열쇠 ''Bingsan-ui Yeolsoe''
|es=Clave Iceberg
}}</div>
{{Project Games notice}}

[[Category:Pokémon Black 2 and White 2]]
[[Category:Game mechanics]]

[[de:Schlüsselsystem]]
[[it:Sistema a chiave]]
[[ja:キーシステム]]
[[zh:钥匙系统]]