Mewtwo has National Pokédex number 150.
Mewtwo is a genetically engineered Pokémon created from the DNA of Mew. In the original games, it is encountered late in the adventure at Cerulean Cave after the player has defeated the Pokémon League and fulfilled other story requirements.
Mewtwo’s number is immediately before Mew’s number 151, which is why the two species are frequently confused. Mew is the mysterious final entry of the original Pokédex, while Mewtwo is the powerful artificial Pokémon placed directly before it.
The character also became the central figure in the first Pokémon feature film, Pokémon: The First Movie – Mewtwo Strikes Back. Its role in both the games and film helped make Mewtwo one of the franchise’s most recognizable legendary Pokémon.