Underfist: Halloween Bash
Underfist is an animated spinoff special of The Grim Adventures of Billy & Mandy. It aired on October 12, 2008. The special was going to be the setup for a new series spin-off of Billy & Mandy, but the contract of Maxwell Atoms with Cartoon Network expired and the special was the finale of Grim Adventures.
Read more about Underfist: Halloween Bash: Plot, Production, Reception