Mewtwo is a Psychic-type Legendary Pokémon, and number 150 in the original Pokédex. Mewtwo is a Psychic Pokémon, and is sometimes used as main antagonist. In the first Pokémon games, Mewtwo can only be captured in the Cerulean Cave.
Mewtwo is the main antagonist in the game. He summons Meowth and the Doomsday gang to destroy Pikachu. He tries to take over the universe, but he failer and gets defeated by Pikachu. He explodes and the Soul Stars disappear too, turning all characters back to good. However, in the post ending, Mewtwo is seen beating up Meowth and the Doomsday Gang for failing.
Mewtwo will be catchable in the game. It will be obtained when the player is in the story. It will be caught in Mt.Chargestone in the lower levels. It can only be opened and passed after obtaining the Gen Trigger. It will be at a level of 40. It can be encountered again if defeated after defeating the Elite 4. But this means it must be caught post-game. It will be at a high-level of 74.
Mewtwo first appeared in the Nintendo GameCube game Super Smash Bros. Melee. Though he is not featured in Super Smash Bros. Brawl, leftover game data shows he was considered as playable once again. Lucario, a new character in Brawl, features a similar attack as Mewtwo did in Melee (Shadow Ball for Mewtwo and Aura Sphere for Lucario) and Mewtwo also appears as a trophy in the game.
Super Smash Bros. Melee - Playable
Super Smash Bros. Brawl - Trophy
Super Smash Bros. for Nintendo 3DS / Wii U - Playable (DLC)