Event 8: Go! Triple Finish!
From SmashWiki, the Super Smash Bros. wiki
Go! Triple Finish! (いくぞ！さんみいったい！, Let's Go! Trinity!) is the 8th solo event match out of a total of 41 in Super Smash Bros. Brawl. This event is a three-on-one battle, pitting the player as Pikachu against a team of Squirtle, Ivysaur, and Charizard. The player is given two stocks, while the computer characters are given one stock each.
Upon completion of this event, the player will receive a CD containing the Road to Viridian City (From Pallet Town/Pewter City) track, which plays on Pokémon Stadium 2.