Amy and her friend, Lissa, don't know what to do about Arnie's bullying, bad-boy behavior, and mean jokes and pranks. The little monster is ruining their lives! The girls decide it's payback time. Total humiliation for Arnie. They find a recipe for green slime on a YouTube channel and mix a big bucket to pour over Arnie at his birthday party. Before their eyes, Arnie's whole body starts to change. The slime turns him into a real monster.