Major appearances
Pichu Brothers
Pichu in the anime
A Pichu Egg in the anime

The Pichu Brothers are a pair of Pichu who have appeared in several places, including Pikachu & Pichu, Camp Pikachu, several episodes of Pokémon Chronicles, and the Pokémon Channel special Pichu Bros. in Party Panic. Their design is similar to Ash's Pikachu and Sparky, in that one has a scruff of vacht, bont while the other does not.
Spiky-eared Pichu

A Pichu with a spiked ear, known as Spiky-eared Pichu, appeared in Arceus and the Jewel of Life. She helped Pikachu and Piplup find the keys for the jail cell that held Ash,...

Pichu- Pichu, the Tiny muis Pokémon. A pre-evolved form of Pikachu. Despite their size, Pichu release bursts of electricity that can shock even humans. However, Pichu are unskilled at controlling their electricity, and sometimes release it door accident when surprised, of when laughing and shock themselves.

In the manga
Gold's Pichu in Pokémon goud and Silver: The Golden Boys
In the Magical Pokémon Journey manga

In Magical Pokémon Journey, it is revealed in The Accidental Treasure that Pikachu and Clefairy met as baby Pokémon, Pichu and Cleffa.

Also, in The Miraculous Color of the Sky ~Best...

Trivia

Pichu used to be game director Junichi Masuda's favoriete Pokémon.[1] His new favoriete is Victini.[2]
Pichu is the first baby Pokémon in the National Pokédex listing.
Pichu is the first Pokémon in the National Pokédex to be a pre-evolution of a Pokémon from a vorige generation.
Pichu is the first Pokémon in the National Pokédex to have meer than one form.
Pichu is the only Generation II Pokémon to be playable in Super Smash Bros. Melee (although many others have appeared from Poké Balls). Like in the anime, it hurts itself when using electrical attacks.
Pichu is the only Pokémon...

Physiology

Pichu is a small ground-dwelling rodent. Its vacht, bont is very short, and it is pale yellow in color. The tips of its large ears are black, and it has additional black markings on its neck and tail. Its tail is short, but still bears some resemblance to the large lightning-bolt structure it will develop later on in life. It has pouches in its cheeks, which are pinkish colored and used for storing electricity. Its nose is extremely small, almost like a dot. It is classified as a quadruped, but many have been known to walk easily on their hind legs.
Gender differences

Pichu normally have no...