Classified as an Electric-type Pokémon, Pikachu is a large yellow mouse with a lightning bolt-shaped tail, and red sacs on its cheek which can generate large amounts of electricity. Overall, it is a cheerful and intelligent Pokémon, but it can be distrustful of its owner. At least some Pikachu are claustrophobic, which prevents it from being contained in a Pokéball, making it difficult to contain. Pikachu is the second evolution form of Pichu, which can evolve into Raichu with the help of the Storm Evolution Stone. Pikachu live in forests, but try to get close to human habitations. They are vulnerable to attacks from ground-type Pokémon.