Mew is a pink, bipedal Pokémon with mammalian features. It has a rounded, wide snout; triangular ears; and large, blue eyes. It has short arms with three-fingered paws and large hind paws with oval markings on the soles. Its tail is long and thin with an ovoid tip. Its fur is so fine and thin, it can only be seen under a microscope. Mew is said to have the DNA of every single Pokémon contained within its body, allowing Mew to learn and use any attack.

As demonstrated by its behavior in the first and eighth Pokémon movies, it shows signs of intelligence, curiosity, shyness, playfulness, and even selflessness. Mew is incredibly adaptable, able to travel freely in the air or underwater. As seen in Pokémon Snap, New Pokémon Snap, and the Super Smash Bros. series, it can create a green, yellow, or pink orb of energy around itself for protection.

According to the radio drama, The Birth of Mewtwo, Mew was discovered by Jessie's mother, Miyamoto, who registered its cry in Guyana Forest 20 years before the events of Generation I. It was worshiped for its protection by indigenous people who created a folk song in its honor and believed it appeared once a year with the rising sun. It wasn't rediscovered until 18 years after Miyamoto met Mew by sunrise on the peak of the highest mountain in a South American mountain range and fell.

Reports found in Cinnabar Island's Pokémon Mansion note scientific expeditions that have sighted Mew in Guyana, South America, the place where it was first discovered. Since Mew can make itself invisible at will, very few people have knowingly seen it, leading some scientists to declare it extinct and most to assume it to be a mirage. It will only show itself to a person who is pure of heart and has a strong desire to see it for themselves. Mew is shown in the anime to be capable of splitting to transform into two Pokémon at the same time.

Mew is the only known Pokémon capable of using the Z-Move Genesis Supernova.

(Source: Bulbapedia)