Mewtwo is National Pokédex number 150 in the original Generation I list.
Mewtwo is a Psychic-type Pokémon introduced in Pokémon Red, Green, Blue, and Yellow. It appears near the end of the original Pokédex, immediately before Mew at number 151. This ordering is one reason Mewtwo and Mew are often discussed together, even though their roles and stories differ.
In the games, Mewtwo can be encountered in Cerulean Cave after the player becomes Pokémon Champion. The Pokémon's story and the first Pokémon movie present it as a powerful artificial creation connected to research on Mew. The game encounter gives Mewtwo a status as an especially rare late-game challenge.
A common mix-up is answering Mew, the mythical Pokémon listed at 151. Dragonite is number 149, while the legendary bird Articuno is number 144. Mewtwo's position at 150 is a stable reference point in the original Pokédex.