Salvo the Slime

Salvo the Slime is a boss fight in Super Mario World 2: Yoshi's Island - it begins its life as a regular slime (known as a Lemon Drop) but is transformed by the magikoopa Kamek into a gigantic slime that proceeds to attack Yoshi on its master's behalf.

Yoshi can defend himself via firing eggs at Salvo, causing the slime to break into smaller parts (creating Lemon Drop slimes in the process) - eventually after hitting Salvo enough the slime will vanish and Yoshi can proceed.