Hoopa

A mysterious Psychic and Ghost-type Mythical Pokémon from Generation VI, this creature possesses a unique ability to transform. While it remains a single-stage Pokémon without evolution, it can shift from its Hoopa Confined state into the powerful, Dark-type Hoopa Unbound by utilizing the Prison Bottle. This massive transformation is temporary, however, as the Pokémon will revert to its original form after three days or under certain specific conditions.