Underfist: Halloween Bash, aka Underfist is a Cartoon Network spin-off movie of the show The Grim Adventures of Billy and Mandy. It was first a joke but Maxwell Atoms's crew and Cartoon Network didn't deny it. Maxwell Atoms did most of the work for the movie since the Cartoon Network crew to work on Underfist was unconfirmed. It is actually the first of the Underfist movie series.