SpongeBob SquarePants/The Grim Adventures of Billy & Mandy

Cast
and more
 * Patrick as Billy
 * Sandy as Mandy (Sandy and Mandy's names rhyme)
 * Plankton as Grim
 * SpongeBob as Irwin
 * Gary as Milkshakes (Gary and Milkshakes are both pets)
 * Wormy as Mr. Snuggles