Mew

Mew is so rare that many experts consider it to be a mirage, as only a few people have seen it. In "Mewtwo Strikes Back" Mewtwo wreaks havoc across the world and awakens the small psychic Pokemon, Mew. A playful little creature, Mew observes others but doesn't get involved, until it discovers the horrible things that Mewtwo is doing. Mew confronts its genetic clone, and a destructive battle of psychic energy begins.

First appearance: Pokemon The First Movie: "Mewtwo Strikes Back"