Event 7: Pokémon Battle
From SmashWiki, the Super Smash Bros. wiki
Pokémon Battle is the 7th event match of 51 in Super Smash Bros. Melee. As an available character of their choice, the player must win a 2 stock match against a CPU Pikachu on Pokémon Stadium, and can only inflict damage or be damaged by hitboxes produced by Pokémon from Poké Balls - hitboxes from character attacks or thrown Poké Balls will harmlessly go through each character, without causing any damage, hitstun, knockback, or hitlag. Poké Balls are the only items that appear. CPU Pikachu has a handicap, and rarely uses attacks; it more often attempts to pursue and use Poké Balls during the match (because its CPU mode is set to ITEM).