Pichu

How Pichu joined the Tourney
Pichu is described as small bipedal mouse with an oval-shaped head and large, black, arrow-shaped ears. The pre-evolutionary form of the popular Pikachu, the Pokédex explains that the electricity pouches on its cheeks are still small and not able to store much electricity yet; because of that, it is not yet skilled at storing electricity. In the game series, as the pre-evolved form of Pikachu, Pichu is less powerful than its evolved counterpart, and can't learn some moves that Pikachu can. However, the only way a player can obtain a Pikachu that knows Volt Tackle is through breeding a Pichu.

How to unlock
The player must complete one of the following requirements to unlock Pichu: For both of these options, the player must brawl Pichu on the Pokemon Stadium III stage. After defeating Pichu, the announcer will say "Someone else has joined the Tourney!" after a Smash Ball appears on the lower-right corner of the screen with a message saying "You can now use Pikachu's pre-evolved form Pichu!"
 * Play 200 multiplayer matches.
 * Complete Event 49: All-Star Match V