|Started||October 12, 2008|
|Ended||October 12, 2008|
Underfist was supposed to be the fourth installment in the Billy and Mandy franchise. However, due to Maxwell Atoms' contract with Cartoon Network expiring, the series was never made. But one special was made and it was called Underfist: Halloween Bash.
The series was supposed to focus on Billy, Mandy, and Grim employing a supernatural crime-fighting organization known as Underfist, which consists of Irwin, Hoss Delgado, Jeff the Spider, Fred Fredburger and General Skarr, who fight monsters and protect the world (or the town of Endsville) from the supernatural forces of evil.
Although the show did have the pilot episode released, the series was cancelled. 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 in 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)
- If this series came to be, it would have been the third spin-off of a Cartoon Cartoon (The other two being The Grim Adventures of Billy & Mandy and Evil Con Carne being spin-offs of Grim & Evil).