Pikachu is a playable Starter
character in Arcade Smash Bros.and makes his seventh return (eighth if you count Ultra in) in the series since Super Smash Bros., being one of the recurring members of the Original 8 alongside with the Hidden 4. He was confirmed two months later when Arcade's got announced after the last fighter of Ultimate's Fighter's Pass Vol. 1. Pikachu is classified as fighter #08. He also has a female counterpart in her Libre costume from Pokémon X/Y.
According to his history, Pikachu was a starter Pokémon specially in Pokémon Yellow. In other installements, he's a wild Pokémon that produces electricity through his red cheeks. Pikachu is the most iconic video game character in the world alongside Mario.
Pikachu is voiced by Ikue Ōtani, voiced since Super Smash Bros. recycled respectively from Brawl, while also providing new clips to female Pikachu with a slightly high-pitched voice and more feminine.