Pichu evolved into Pikachu in Brawl
One source states, "Pichu may have made only one appearance as a playable fighter in Super Smash Bros. Melee, but some fans believe that it technically made it into Brawl as well. How can this be? Well, many believe that this Pichu evolved into the Pikachu from Brawl.
There is actually some evidence to support this, such as the fact that Pikachu's Final Smash is Volt Attack, which can only be learned by an egg-born Pichu. Also, both Pikachu and Pichu wear the same blue goggles in both games.
So while it has never been explicitly said that this was meant to be the case, it definitely looks like some seeds were subtly planted in order to create some continuity between the two games"(Jacobs).
