Pichu (ピチュー, Pichū) is a fictional creature from the Pokémon media franchise, in which it is the pre-evolved form of Pikachu. It appears as a playable character in Super Smash Bros. Melee but did not return to Super Smash Bros. Brawl as one along with four other characters but appears as a trophy.
Pichu is described as small bipedal mouse with an oval-shaped head and large, black, arrow-shaped ears. As it is the pre-evolutionary form of Pikachu and a baby Pokémon, the Pokédex explains that the electricity pouches on its cheeks are still small and not able to store much electricity yet. It may discharge power accidentally and spontaneously if amused or startled, and vice versa. Despite its small size, it can zap even adult humans, but it surprises itself whenever it does so. When it plays with other Pichu, they may short out electricity with each other, creating a shower of sparks, startling them and causing them to start crying. It gets better at holding power as it grows older, where it starts playing with other Pichu by touching tails and setting off sparks in apparent mutual tests of courage. It charges itself with electricity more easily on days that either have very dry air or has thunderclouds, in which case the crackling of static electricity can be heard coming off of it.
In the games, Pichu only evolves into Pikachu when it reaches a certain level of happiness with its Trainer. Its Pokédex description claims that it is inexperienced with its ability to handle electric-attacks and occasionally inflicts damage to itself, though this does not actually occur in the Pokémon games. It however, has been demonstrated in both the Pokémon animated TV series and in Super Smash Bros. Melee.
In the game series, as the pre-evolved form of Pikachu, Pichu is less powerful than its evolved counterpart, and can't learn some moves that Pikachu can. However, the only way a player can obtain a Pikachu that knows Volt Tackle is through breeding a Pichu.
 In Super Smash Bros. Melee
 As a playable character
Pichu is a playable unlockable character in this game, albeit as one of the weakest characters, but faster and slightly stronger. Melee is notably the only game that is true to Pichu's Pokédex description of harming itself with its own electrical energy: whenever Pichu performs an attack that involves electricity, it takes a few percentage of damage. It is also the lightest character in Melee. It is ranked 25th on the Melee tier list in F tier, at the second lowest spot.
 Trophy Description
A Tiny Mouse Pokémon identifiable by its big ears, Pichu evolves into Pikachu. It's not very skilled at storing up electrical energy and will sometimes discharge it if jarred. Although it's small, it has enough electrical power to give even an adult quite a shock. It's often startled by its own power.
 In Super Smash Bros. Brawl
 As a Trophy
Pichu makes a appearance in Brawl as a collectible trophy. It is obtained by completing All Star mode without using a continue. Pichu and Mewtwo were the only two non-returning Melee characters to have trophies in Brawl, and neither trophy description makes any reference to their appearances in Melee in much the same way that none of the main character trophies in Melee and Brawl make any reference to their appearances in any Smash games.
A Tiny Mouse Pokémon. Because its electric cheek pouches are still small, it cannot store electricity yet. Pichu has been known to flaunt its courage by touching tails with others and setting off sparks. It is easier for Pichu to build up electricity when the humidity is lower. Pichu will evolve into Pikachu.