Mew was added to Pokémon Red and Green as a last-minute inclusion.
Mew is listed as National Pokédex number 151, after Mewtwo. It was not part of the ordinary collection path in the original games and was intended for a later promotional activity. Because its data existed in the games but it was not normally obtainable, rumors about the mysterious Pokémon spread among players.
In 1996, CoroCoro Comic announced a promotion involving Mew. Twenty winners were selected from entrants, and the Pokémon was uploaded to their game cartridges. This unusual distribution helped turn Mew into a legendary secret and encouraged interest in trading and Pokémon news.
Mew is often confused with Mewtwo because their names and designs are related. Mewtwo is a major story Pokémon and appears in the first animated film, while Mew is the hidden Mythical Pokémon associated with the original games’ special promotion.