Mew was offered through the 1996 CoroCoro magazine lottery.
Mew was a secret Pokémon added late in the development of the original games. It could not normally be obtained through standard gameplay, which made its existence a powerful mystery for early players.
A CoroCoro Comic promotion announced the Legendary Pokémon Offer in April 1996. Readers sent postcards, and 20 winners were selected at random. The winners sent in their cartridges so Mew could be uploaded to them, turning a rare game secret into a highly publicized event.
The promotion helped fuel word-of-mouth around Pokémon. It also contributed to the game's early momentum: sales of Pocket Monsters Red and Green had surpassed one million copies by September 1996. Mew is numbered 151, after Mewtwo, in the original Pokédex.