Mew is National Pokédex number 151.
Mew is a Psychic-type Mythical Pokémon and the final entry in the original National Pokédex. Its mysterious status helped make it one of the most sought-after Pokémon in the early games, even though it was not normally obtainable through standard gameplay in Pokémon Red, Green, and Blue.
Mew is closely connected to Mewtwo in the franchise’s fiction. Mewtwo was created from genetic material associated with Mew, and their relationship became central to Pokémon: The First Movie. Despite that connection, they occupy separate Pokédex entries: Mew is 151 and Mewtwo is 150.
The number 151 is sometimes mistaken for the number of Pokémon available through ordinary game progression, because Mew was distributed through special events rather than regular encounters. The original Kanto Pokédex therefore ends with Mew as its hidden final entry.