Mewtwo is Pokédex number 150 in the original National Pokédex.
It is the final numbered species in the first-generation Pokédex, immediately before Mew at number 151. In Pokémon Red and Blue, Mewtwo can be encountered in Cerulean Cave after the player defeats the Elite Four and the rival. Its backstory describes it as the result of genetic experiments based on Mew.
Mewtwo is a Psychic-type Legendary Pokémon. Unlike Mew, which is associated with the ancestry of many Pokémon in the games' lore, Mewtwo was artificially created. The name also reflects that relationship: “Mewtwo” identifies it as a second, engineered counterpart to Mew.
Mewtwo is often confused with Mew because the two species are connected and occupy adjacent Pokédex numbers. They are separate Pokémon, and Mewtwo is not an evolution of Mew. Later games also gave Mewtwo two Mega Evolutions, Mega Mewtwo X and Mega Mewtwo Y.