Yowser is a boss in Super Mario 64 Bloopers: The Videogame, fought in The Borough.
Yowser mainly throws Spike Shells (Blue Shells) as a primairy attack. The goal is to kick these back to him until he dies. When he has less HP remaining, he'll try to shoot the spikes on his shell to the character. Since Mario is the only one who can kick, he's required to fight Yowser. Upon defeat, Yowser chokes.