Hoopa

Hoopa is a Mythical Pokémon introduced in Generation VI. Its default Hoopa Confined form is Psychic/Ghost, while using the Prison Bottle changes it into the Psychic/Dark Hoopa Unbound. Hoopa is not known to evolve into or from another Pokémon, and the Unbound form will revert to Confined if it is in the party and three days have passed since changing to Unbound. Other circumstances may also cause reversion.