2x11 - The Grim Adventures of Billy and Mandy

After Grim fails to pull a werewolf out of his hat, Irwin is bitten by said werewolf. Billy takes Irwin as his new pet dog, naming him Sprinkles, and enters him in the Endsville Dog Show to compete against Mandy's dog, Saliva. At the contest, Sprinkles is about to win, so Grim releases a "were-flea" whose bite causes the werewolf to revert to a naked Irwin. It appears that Irwin won the contest anyway.