Pichu (ピチュー, Pichu) is a fictional creature from the Pokémon series. It debuted in the series' second generation, and represents that generation as a playable character in Super Smash Bros. Melee and Super Smash Bros. Ultimate after being absent from both Super Smash Bros. Brawl and Super Smash Bros. 4.
Pichu is a small, rodent-like Pokémon characterized by its yellow fur, flat, triangular ears, and pink cheeks. It is categorized within the Pokédex at #172 as the "Tiny Mouse Pokémon". As both the pre-evolved form of Pikachu and a baby Pokémon, Pichu is much less powerful than its evolved forms. While it cannot learn some moves that Pikachu and Raichu can, it can learn three moves (Charm, Sweet Kiss and Nasty Plot) that its evolved forms cannot. Pichu only evolves into Pikachu when it achieves a very high level of friendship with its Trainer.
The Pokédex explains that the electricity pouches in Pichu's cheeks are still small and unable to store much electricity. This, in turn, makes it inexperienced with handling electrical attacks, to the point that it occasionally inflicts damage to itself. While this does not actually occur in the Pokémon games (outside of two instances where it is a universal mechanic), it has nevertheless been demonstrated in both the Pokémon anime and the Super Smash Bros. series.
Pichu's inexperience with handling electricity may also result in spontaneously discharging if amused or startled. Despite its small size, it can zap even adult humans, but 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.
Pichu becomes more adept at storing electricity as it grows older, and will start playing with other Pichu by touching tails and discharging sparks in apparent mutual tests of courage. It charges itself with electricity more easily on days that either have very dry air or thunderclouds, in which case the crackling of static electricity can be heard coming off of it.
Like Pikachu, Pichu has a special variant of its species; in Pichu's case, it is Spiky-eared Pichu, which debuted in Pokémon HeartGold and SoulSilver Versions. True to her name, Spiky-eared Pichu features three spiky tufts of fur on her left ear. Spiky-eared Pichu also deviates from other members of her species by knowing Helping Hand and Pain Split, having different Pokéathlon stats and, most notably, her inability to evolve or be traded outside HeartGold and SoulSilver Versions and her incompatibility with the Poké Transfer by extension. The latter two traits are later explained by Professor Elm as a side effect of her constantly traveling through time with Celebi.
As a playable character
Main article: Pichu (SSBM)
Pichu is a playable unlockable character in Super Smash Bros. Melee. As confirmed in a development news update shortly after Melee's release, Pichu is a "joke character" because of its status as an overwhelmingly inferior clone of Pikachu that possesses many significant weaknesses. Its most infamous flaw is based on its Pokédex description of unintentionally harming itself with its own electricity: whenever Pichu performs an electrical attack, it will sustain 1%-4% recoil damage. Along with this, Pichu is the lightest character in Melee, giving it extremely poor endurance. Due to its glaring weaknesses, Pichu is ranked 24th out of 26 on the Melee tier list, placing it in the G tier.
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.
Pichu is one of the five playable characters in Melee who did not return as a playable character in Super Smash Bros. Brawl. It is also the only character who neither has unfinished data on Brawl's disc, nor a new playable character as a successor. Instead, Pichu only appears as a trophy. However, its ability to wall jump and the blue goggles from its blue alternate costume were given to Pikachu.
Pichu makes an appearance in Brawl as a collectible trophy. It is obtained by completing All-Star Mode without using a continue. The trophy describes Pichu's appearance in the Pokémon games, and makes no reference whatsoever to its appearance in Melee:
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.
Once again, Pichu only appears as a trophy in Super Smash Bros. for Nintendo 3DS, while Super Smash Bros. for Wii U references it via Palutena's Guidance regarding Pikachu. Once again, Pikachu still has Pichu’s blue googles and Pichu’s wall jump.
As a playable character
Main article: Pichu (SSBU)
After a two installment absence, Pichu returns as a playable character in Super Smash Bros. Ultimate. This marks its first playable appearance in the series in 17 years, a distinction shared with fellow Melee newcomer Young Link. Spiky-eared Pichu makes its first appearance in a game in 9 years as an alternate costume of Pichu, though unlike Pikachu Libre, Spiky-eared Pichu does not appear as a Spirit.
Pichu still functions as a lighter, polarized clone of Pikachu, yet it has nevertheless been marginally decloned, thanks to a number of its moves having slightly modified animations and/or marginal lag decreases, as well as Pikachu gaining a new neutral aerial. It has also been greatly buffed, due its previous status as a "joke character", and is considered by many a top-tier character, even with its recent nerfs in updates. Despite the term "Echo Fighter" being used in Ultimate to denote clones, Pichu is not labeled as such, and no official reason has been given for this oddity. However, it is worth noting that any clone characters introduced before Smash 4 are not labeled as Echo Fighters.