|Started||October 12, 2008|
|Ended||October 12, 2008|
Underfist is a unmade spin-off show of The Grim Adventures of Billy & Mandy (and Grim & Evil), however due to Maxwell Atoms's contract with Cartoon Network expiring the series was never made. But one special movie was made and was classed as the final episode of The Grim Adventures of Billy & Mandy, the episode was called Underfist: Halloween Bash.
This series picks up where the original left off. Instead of focusing on Grim, Billy and Mandy, it is about the trio employing a ragtag group of crimefighers who go about saving the world (or the town Endsville) from monsters known as Underfist, which consists of Irwin, Hoss, Jeff, Fred Fredburger and General Skarr.
Although the show did have the first/pilot episode released, the series was canceled. Although it was believed that due to the credits in Underfist: Halloween Bash that a few more were planned with names and plots and though these credits and work from Maxwell Atom's blog, it shows that there was more episodes and characters planned for a release.
- Underfist Versus The Dinosaurs (seen it the credits of Underfist: Halloween Bash)
- Underfist Against the Astrovampires (seen it the credits of Underfist: Halloween Bash)
- There was a few more episode titles shown in the credits but they look more like joke episodes from their titles.
- Naughty Eris & Nice Eris (seen it the credits of Underfist: Halloween Bash and some of Maxwell Atom's work)
- Lord Malefactor (Seen in some of Maxwell Atom's work)
- Nephthys (Seen in some of Maxwell Atom's work)
- Boogersnatch King of the Squid Demons (Seen the end of Underfist: Halloween Bash and in some of Maxwell Atom's work)