Mew

Mew is a Psychic type Pokemon. It is not known to evolve into or from any other Pokémon. N.B: Sam has stated that Mew will be available in the game at some point.

Description
Mew is normally described as a pink cat-like creature, though its morphology is actually more like a jerboa. Mew's hair is so fine and thin, it can only be seen under a microscope. It has a long, skinny tail. Mew has big hind legs, like a rabbit, and short arms with three-fingered paws. Mew has triangle-shaped ears and baby-blue eyes. Mew is said to have the DNA of every single Pokémon contained within its body. It also vaguely resembles an embryo or fetus, and is often depicted in a pink orb.

Move Set
Level 1: Pound

Level 1: Reflect Type

Level 1: Transform

Level 10: Mega Punch

Level 20: Metronome

Location
Buying the Hero Edition of Ninja-Ja.

Trading with another account (after 2.6)

Shiny
Shiny Mew used to be available through donations in earlier stages of development, but it was removed due to trolls.

Now, however, buying the "Hero Edition" of Ninja-ja will grant you 3 shiny Mew codes.

The only way to ever get a shiny Mew will be to trade/buy it, however you can still get a normal Mew at some point in the game.

Trivia

 * In many of the games, Mew is depicted as pink. However, in the movies and some of the spin off games, Mew is a much lighter color.
 * Unlike most legendary Pokemon, Mew needs only 1,059,860 Exp. to get to level 100, whereas most legendary Pokémon need 1,250,000.