Mewtwo

Mewtwo is a Psychic type Legendary Pokemon introduced in Generation I. Mewtwo can Mega Evolve into either Mega Mewtwo X or Mega Mewtwo Y.

Despite being genderless, Mewtwo has a gender in both of their Smash Bros. appearances, in Super Smash Bros. Melee as an unlockable character and in Super Smash Bros. for Nintendo 3DS and Wii U as a downloadable character.

Trivia

 * Mewtwo was one of the most suggested Pokemon for Super Smash Bros., the others being Blaziken and Lucario, which both have dual Fighting type.
 * Mewtwo was supposed to appear in the first game and the third game, but in both occasions Mewtwo failed to qualify.