The Grim Adventures of Billy and Mandy Wiki
Underfist: Halloween Bash
Underfist Halloween Bash Endcard.png
Series Underfist
Season Special / Pilot Episode
Writer Maxwell Atoms
Broadcast information
Cartoon Network US Premiere October 12, 2008
Chronological information
The Grim Adventures of the KND

Underfist: Halloween Bash (shortened to Underfist and advertised as Billy & Mandy: Underfist) is a spin-off special of Grim & Evil. It aired on October 12, 2008. The special was going to be a setup for a new series, but Maxwell Atoms’ contract with Cartoon Network had expired before the series could be green lit, so the special was the official series finale, not "Heartburn."


On Halloween night, Irwin, Billy, Mandy, and Grim are trick-or-treating. Billy, Mandy, and Grim decide to go home after having no success with Dracula, who rudely hands them pennies. Irwin tries to stop Mandy from going by saying how their lives are passing them by but after after Mandy threatens him, Irwin decides to Trick or Treat alone.

Irwin tries to ask for candy in Hoss's trailer but Hoss thinks Irwin is a real vampire (which he is) due to his costume and almost tries to stab his heart with a stake, but Irwin explains to him that it's Halloween, and after Hoss looks around and notices that it is in fact Halloween, he goes back to his trailer, not before warning Irwin that he has his eye on him, he then tries to go to General Skarr's house. But General Skarr, (peeking from the blinds of his window) angrily yells at him to get off his lawn, after that, he tries to visit other houses, but he gets weirded out by Jeff playing with Fred Fredburger by spraying him with light blue webs that he got from eating blue jelly beans.

Right after he gives up trying to trick or treat, Mindy (secretly turned into a witch by an evil marshmallow bunny named Bun Bun) fools Irwin into opening an Underworld portal releasing an army of evil candy warriors and Bun Bun, where they start terrorizing the neighborhood. Irwin gets attacked and contacts Hoss Delgado, who helps him with the battle. The warriors take down Hoss with soda-candy guns, which if Hoss gets sticky, he gets a rash. When they kill Skarr's winning purple pansies, he comes out of his garage with a robot, joining the battle. Soon it's an all out war, with no mercy, no rules, no nothing. Mindy again tricks Irwin, but this time, pretending she is being kidnapped by Bun Bun, taking her into the Underworld.

When the candy level gets to high, Hoss clicks his car unlock system, which a giant saw car (spoof of the Gotengo from Godzilla: Final Wars) comes drills out of the ground. They escape and start to plot their attack to the Underworld.

Soon they find a portal to the Underworld in the rain, which Hoss and Irwin jump in first (because he does not trust monsters and says to Skarr that he doesn't trust one eyed weirdos), but the portal turns off, because it is controlled by a diamond, which Mindy (in her witch form) smashes. The candy warriors try to sacrifice Hoss, by pushing him into hot coco, but they want to leave Irwin alive. This is because he has the powers of a mummy, which they need to keep the balance of the Underworld in place, and to become stronger warriors to eat the trick-or-treaters.

Mindy creates a potion which turns all the warriors into candy monsters, and all she needs now is Irwin's powers to create the candy warriors ultimate monster form. But Irwin refuses.

Soon Jeff, Fred, and Skarr find out a way how to get to the Underworld by using Hoss's car to drill into the Underworld, and they rescue Irwin and Hoss.

The Underfist Team

But the army of candy monsters hasn't given up yet. They head to the city and attack. Irwin and Hoss get into an argument, leading into a battle, turning on each other. While the battle is going on, the monsters suck up Irwin's power (but not all of it) and transform into one giant candy monster. Jeff and Fred try to escape, but they fail. Soon Hoss and Irwin see the monster and start to fight it, beating it. Irwin discovers that Hoss is scared of monsters, because he was haunted as a kid. In a rare moment of emotion for himself (and the franchise itself), Hoss apologizes to Irwin for how he treated him and realizes there are good monsters out there. Mindy also realizes what she did was wrong and apologizes as well. 

Just then, Bunn-Bunn appears and admits that he was the one who turned Mindy into a witch and used her to get to Irwin so he could use his powers to open up portals to the Underworld. He also reveals that he cut off Fred's tusks, made Billy scared of spiders, and haunted Hoss's childhood. Just as Bunn-Bunn is about to kill Mindy and Underfist, General Skarr kicks Bun Bun into hot coco, melting the marshmallow bunny, and saving the world and Halloween.

Grim, Billy, and Mandy award Underfist for saving Halloween, but then they hear something outside and investigate. It's soon revealed that there is an army of squid warriors who have found their way to the surface world that the team made while trying to escape from the Underworld.

Final Appearance of Characters




Click here to view more images from Underfist: Halloween Bash.
The image gallery for Underfist: Halloween Bash may be viewed here.

Continuity/animation errors

  • When Hoss comes out of his trailer, he punches Perkins's face off, but later Perkins is fine.
  • Hoss is stated to be 48 instead of 33. Although it could be due to a time skip between Grim Adventures and Underfist, it's unlikely as no one else has aged, or Hoss possibly lied about his true age.
  • Hoss is said to have gone into depression due to his breakup with Eris, even though that wasn’t the case in the episodes after they broke up.


  • Chowder and Courage the Cowardly Dog made a cameo on a Halloween float.
Wishbones Skull Cameo.png
  • Thromnambular makes a cameo in Grim's lab but with 13 wishes on his forehead, instead of 9.
  • This is technically the series finale for The Grim Adventures of Billy & Mandy.
    • This special was also the pilot for the planned Underfist series, but due to Maxwell Atoms' contract with Cartoon Network ended around the time of the special's premiere, as well as Cartoon Network wanting more live action shows than animated shows at the time, the plans for the rest of the series was cancelled.
  • Fred was redesigned to a peanut shape. He is more green and smaller.
  • There were supposed to be more sequels shown at the ending credits of Underfist: Halloween Bash. The sequels in order are "Underfist Vs. the Dinosaurs", "Underfist Against the Astro-Vampires", "Underfist: Easter Beatdown", "Underfist: Return of the Spider Queen", "Underfist: Action Squad Miami", "Underfist Teaches Traffic Safety", and "Underfist Babies". However, none have ever been produced.
    • Maxwell Atoms has stated that some of the sequels were simply jokes, but that at least the first two were actually planned.
  • General Skarr seems to show signs of aging, as he now has a beard, mustache, and his military clothes are absent in the film (he's either in his underwear or in his Underfist uniform).
    • Additionally, Hoss has also aged: he has grey streaks in his hair, he's put on weight, and it's confirmed that he's 48 years old in the movie (as opposed to being in his thirties in the series). He also lost his right leg and replaced it with a chainsaw, similarly to his right hand.
    • Despite this, Irwin, Billy, and Mandy don’t appear to have aged at all.
  • During the opening sequence narrated by Grim, clips from previous Billy & Mandy episodes are used as follows: the Billy & Mandy main title sequence, "Be A-Fred, Be Very A-Fred", "Wrath of the Spider Queen", "Guess What's Coming to Dinner", "Wishbones", "That's My Mummy", "Irwin Gets a Clue", "Home of the Ancients", "King Tooten Pooten", "Dracula Must Die!", "Billy & Mandy's Jacked Up Halloween", and "Billy & Mandy's Big Boogey Adventure".
  • Baron Von Ghoulish, from the episode "Billy and Mandy Save Christmas", makes a brief cameo in the film. He is seen being scared by Trick-or-Treaters in costumes, and falls back into his coffin.
  • Jeff makes two references to Maxwell Atoms when says, “Soon [he] will be thirty eight” and “[He] will get a job [he] hates.”
  • We learn how Hoss lost his hand, leg, and eye; he explains the he was running with scissors, despite what his mother told him.
  • The lab coat Billy wears while on his "B" alter-ego look similar to Dexter's clothes from Dexter's Laboratory.
  • Fred Fredburger is the only Underfist member that didn't debut in the Grim & Evil era.
  • The characters who make up Underfist are all side characters who started gaining popularity after appearing in the series (sometimes called "Ensemble Darkhorses"). This is most likely why they were chosen as the main characters and Grim, Billy, Mandy, and Mindy are secondary characters this time.
    • Irwin was, arguably, the most popular of these characters, as he started gaining larger roles as the series progressed. This is probably why he is the main protagonist. 
  • According to Maxwell Atoms, he initially approached online artist Vinson "Bleedman" Ngo, known for creating a fan-comic inspired by Billy & Mandy entitled Grim Tales, for character design work on the special, but he declined due to commitments with his own work.[1]