Deoxys

Deoxys (Japanese: デオキシス Deoxys) is a Psychic-type Mythical Pokémon introduced in Generation III.

While it is not known to evolve into or from any other Pokémon, it has three other Formes. In Generation III, its Forme depends on which game cartridge it is on and cannot be changed without trading. In later generations, its Forme can be changed at will in Veilstone City, Kanto Route 3, Nacrene City, Ambrette Town, Fallarbor Town, or Hokulani Observatory.
 * Normal Forme is the default in Pokémon Ruby and Sapphire and Pokémon Colosseum and XD.
 * Attack Forme is the default in Pokémon FireRed.
 * Defense Forme is the default in Pokémon LeafGreen.
 * Speed Forme is the default in Pokémon Emerald.