Mew was secretly added to Pokémon Red and Green after the main development work was complete. It became the hidden 151st Pokémon of the first generation.
The development team inserted Mew into unused space after debugging was finished. Because Mew was not normally obtainable through standard gameplay, Nintendo did not initially publicize its presence in the same way as the other original species.
Mew’s existence became a powerful rumor among players. Official distributions and special events later gave players legitimate ways to obtain it, turning the mysterious Pokémon into a major part of early Pokémon culture.
Mew should not be confused with Mewtwo. Mew is a small, pink, Mythical Pokémon associated with the genetic origins of many Pokémon, while Mewtwo is a powerful artificial clone created from Mew’s genetic material. Mew’s Pokédex number is 151, immediately after the original 150 species.