Mew

Mew is a mythical Psychic-type Pokémon first introduced in Pokémon Red and Green Versions (Pokémon Red and Blue Versions in regions outside Japan). Mew is said to contain the DNA of all Pokémon, allowing it to learn nearly any move that isn't exclusive to one Pokémon group of Pokémon.

In the Super Smash Bros. series, Mew has appeared in every installment to date. It can be summoned from a Poké Ball (and in Super Smash Bros. for Nintendo 3DS / Wii U a Master Ball), and when it is summoned it says its name and flies up off the screen, its effect differing by game. It gives the player a score bonus at the end of a match in Super Smash Bros. and Super Smash Bros. Melee, and has a one in 251 chance of appearing. In Super Smash Bros. Brawl it drops as CD (or a Sticker if the player has every CD) and has a one in 493 chance of appearing. Finally, it drops a custom part or a Trophy in Super Smash Bros. for Nintendo 3DS / Wii U, though it may also drop a CD in the Wii U version.