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Cerulean Cave and the postgame ceiling

Mewtwo (Pokedex slot 150) is the lab-grown genetic clone of Mew, encountered at level 70 inside the Unknown Dungeon in Cerulean City — a postgame area locked until the player defeats the Elite Four and Champion. The species cannot be obtained through trade or breeding from any cartridge; the only legitimate copy in Pokemon Red, Green, Yellow, and the Generation III remakes Pokemon FireRed and LeafGreen is the level-70 wild encounter. The character was designed by Ken Sugimori with bipedal posture, a kangaroo-style lower body, an armoured neck, and a thick tail that conceals an interior neural conduit in the official anatomy artwork.

The First Movie and the antihero arc

Pokemon: The First Movie (Mewtwo Strikes Back, July 1998 in Japan, November 1999 in North America) established Mewtwo as the franchise's first true antihero, voiced in English by Philip Bartlett (also credited as Jay Goede) and in Japanese by Masachika Ichimura. The film follows Mewtwo's escape from the Aether Foundation predecessor Team Rocket laboratory and his vendetta against trainers, culminating in a New Island clone-battle climax that the film's editing controversially trimmed for the English-language release. Mewtwo returned as the protagonist of the 2000 sequel Pokemon: The First Movie: Mewtwo Returns and the 2013 special Mewtwo: Prologue to Awakening.

Competitive role and franchise prominence

Mewtwo's base Special Attack of 154 — combined with movepool access to Psystrike, Aura Sphere, Ice Beam, and Recover — placed the species in the Ubers competitive tier on first release and has kept it there across every Smogon-organised generation since. Mega Evolutions Mega Mewtwo X (Psychic/Fighting) and Mega Mewtwo Y (Psychic, with the highest Special Attack of any Mega Pokemon at base 194) were added in Pokemon X and Y (2013) and remain among the franchise's most powerful single-target attackers. Mewtwo has appeared as a playable fighter in Super Smash Bros. Melee (2001), Brawl (2008 via 4 DLC patch), 4 (2015), and Ultimate (2018), retaining the same Psycho Break special across the entire run.