Prince Froggy

Prince Froggy is a boss found in Super Mario World 2: Yoshi's Island and is actually one of the game's more unique fights, Prince Froggy is actually a normal frog but becomes an enemy of Yoshi after Kamek shrinks him to the size of an insect - prompting Prince Froggy to eat him.

Once inside Prince Froggy's stomach Yoshi must use his eggs to hit the frog's uvula repeatedly until Yoshi manages to escape - although he doesn't die Prince Froggy definitely had one of the more painful boss encounters in the game (alongside Hookbill the Koopa)