Mew was hidden in the original Pokémon Red and Green games and later revealed to spark interest.
Mew was not part of the ordinary planned capture journey. The development team placed it in unused space in the cartridges after final debugging, making it obtainable only through special distributions or unusual methods. Its secret status generated rumors and encouraged players to keep investigating the games.
Mew is distinct from Mewtwo, which appears as a major legendary Pokémon in the game's story and in the first movie. Mew is the ancestor-like Mythical Pokémon associated with Pokédex number 151, while Mewtwo is number 150.
The hidden Pokémon became an important early example of how mystery and word of mouth could extend a game's life. It also helped establish Pokémon's tradition of event distributions and rare Mythical Pokémon, a legacy still visible as the franchise reaches its 30th anniversary.