Underfist, also called Underfist: Halloween Bash is an animated special of The Grim Adventures of Billy & Mandy meant to be setup for a Spin-Off of the show, but the project never went through due to Maxwell Atoms' contract with Cartoon Network expiring. Instead, it serves as the Grand Finale to Billy and Mandy, along with the Grim & Evil franchise as a whole.

The special aired on October 12, 2008 and features Irwin, Hoss Delgado, Skarr, Jeff the Spider, and Fred Fredburger teaming up to fight an army of candy from the Underworld.

Tropes:

• 2D Visuals, 3D Effects: The pumpkin tanks and the shot of the giant chocolate bar mummy monster forming.
• Accidental Misnaming: Hoss constantly towards Irwin, much to the kid's eventual irritation since they’ve met before twice in the show, and Irwin was even his sidekick once. Hoss cops to the fact that his memory isn't too good. He briefly gets it right during the climax, only to go back to forgetting afterwards.
• And the Adventure Continues: The special ends with Underfist preparing to fight another villain named Boogersnatch and his army of squid monsters.
• Anything but That!: Because the candy soldiers' soda rifles made his clothes all sticky, Hoss declares he'll be fighting naked from now. The candy soldiers surrounding him immediately surrender rather than deal with that.
• Are You Pondering What I'm Pondering?: Jeff and Fred were watching, as Hoss and Skarr fight waves of candy monsters. It takes a while for only one of them to realize this is a serious situation.
  Jeff: You know something, Fred?
  Fred: Yes! I know where babies come from!
  Jeff: [awkwardly] Okay. But I mean that I don't think there are supposed to be fireworks on Halloween. In fact, I think Hoss Delgado and Mr. Skarr might need our help.
• Attack Of The 50 FT Whatever: Mindy at one point merges all of the trick-or-treater eaters together to form a giant comprised of chocolate.
• Behind the Black: Hoss briefly hides from the giant chocolate bar with lollipop hands by cowering behind the stylistic widescreen bars.
• Big Bad: Mindy at first appears to be the main villain, but she's actually a pawn of Bun-Bun.
• Big Damn Heroes: Fred Fredburger and Jeff save Hoss and Skarr from the stronger candy mooks, though not before Fred spells his name.
• Big "WHY?!": Sperg, while getting a wedgie from one of the candy monsters.
• Bookends: The special begins with Dracula giving Billy, Mandy, and Irwin pennies as Halloween candy, and ends with Dracula receiving a penny instead of a medal.
• Breaking the Fourth Wall: Irwin at one point comments how he was Hoss Delgado's sidekick in one episode of Billy & Mandy. He also questions why a marshmallow bunny is in a Halloween special.
• Call-Back: Irwin sees Hoss as a macho role model, reminding Hoss he became his sidekick in the episode, "Irwin Gets a Clue", from the TV series.
• The Cameo: Several characters from the Billy and Mandy cast, including Billy, Mandy, Grim, Billy's parents, Sperg, Dracula, Grandmama, Nergal, and his family.
  • A cameo by Jack O'Lantern was planned (as a scarecrow behind Mindy when she says "Ha-ha! You looked!◊), but ultimately cut.
  • Chowder and Dee Dee can be seen in a pumpkin float near the beginning of the special.
  • Thromnabular from the episode "Wishbones", can be seen in Grim's lab, with 13 wishes on his head.
  • Baron Von Ghoulish, from the Christmas special, makes a cameo in Mindy's song as a monster who is scared by kids in costumes.
  • A drawing◊ of Boskov and Hector Con Carne can briefly be seen during a portion of the song "I Don't Wanna Grow Up".
  • The Boogey Man appears as the head of a flying Pez Dispenser.
• Chekhov's Gun: The Candy Blaster gun that destroys one entire piece of candy. It shoots out Billy, who immediately devours the giant candy monster.
• Cloudcuckoolander's Minder: Jeff towards Fred. While Jeff has his own childish moments, he's far more grounded, and he often keeps Fred focused as best as possible.
• Damsel in Distress:
  • Mindy is kidnapped early on, but it's later subverted when she's revealed to be in league with the Big Bad.
  • Played Straight with the president aka Mandy.
• Destructive Savior: After repelling the first wave of the invasion, Hoss says it was done with minimal damage. Surveying the sheer destruction all around them, Skarr makes light of this preposterous statement.
• Demoted to Extra: Billy, Mandy, and Grim are all demoted to minor roles in this special.
• Doom Troops: Mindy mutates the chocolate bar Mooks into much stronger "trick-or-treater eaters".
• The Dragon: Bun-Bun appears to be Mindy's second-in-command.
  • Dragon-in-Chief: However, Bun-Bun is shown to be much more competent than Mindy, and the one who came up with the Evil Plan in the first place. He's also The Man in Front of the Man.
  • Bun-Bun also later gains a dragon in the form of Skarr. However, Skarr was faking being on his side the whole time.
• Driving Stick: When Hoss Delgado summons his car—a tank with a giant fist on the end—Irwin asks Hoss why he has never driven it before. Hoss explains that he doesn't drive stick. Jeff then thinks back to a time he was playing with a wooden stick in place of a toy car, then confidently declares that he can drive stick.
• Elite Mook: While battling the chocolate bar soldiers, Hoss encounters a much stronger chocolate bar with lollipops for hands.
• Entitled Bastard: After Mandy gives all the members of Underfist gold medals for saving the world, Dracula asks for a medal, too, even though he did literally nothing to help.
• Fake Defector: Skarr becomes The Dragon to Bun-Bun, only to betray him right when he's about to kill our heroes.
• Fake-Out Fade-Out: Roughly five minutes into the special, Irwin gives up on his Halloween night and heads home. Cue the camera zooming out past Endsville and the Earth, while a song about giving up plays and fake credits roll. The credits are then interrupted by Mindy asking Irwin for help, at which point the scene rewinds back to Irwin.
• For the Evulz: Bun Bun isn't given much motivation for scaring Hoss when he was little, making Billy afraid of spiders, cursing Mindy into becoming a witch, and sawing off Fred Fredburger's tusks. He seemingly did all of that out of pure sadism. He isn’t even given a reason for wanting to Take Over the World, besides simply because he’s evil and power-hungry.
• Freudian Excuse: Hoss hates monsters because a monster scared him when he was little and made him wet the bed for thirty years.
• Gasshole: Mindy becomes one after becoming a witch. Her farts are strong enough to put people to sleep.
• Genre Shift: From the horror-comedy of The Grim Adventures of Billy & Mandy to action-comedy.
• Good News, Bad News: After Irwin wakes up in the truck, Hoss tells him the good news is that a new President has been elected and restored a good deal of order to the world. The bad news is that Bun-Bun has kidnapped this new President. The worse news is that Irwin is expected to join Hoss on the rescue mission.
• Grammar Nazi: Bun-Bun boasts he will "once and for all permanently" deal with Hoss. When Irwin points out that statement is needlessly redundant, Bun-Bun makes light of his grammar being corrected at a time like this.
• Here We Go Again!: Just as Underfist is being awarded for saving Halloween at the end of the special, an army of squid warriors have found their way to the surface, which the team prepare to fight.
• Hypocritical Humor:
  • Hoss Delgado doesn't trust "one-eyed weridos" despite the fact that he himself only has one eye.
  • In the beginning of the movie, Dracula gives Billy, Mandy, and Irwin pennies instead of candy when they come to his house, trick-or-treating. In the end, when Mandy gives Dracula a penny instead of a gold medal, Dracula is displeased and says that pennies are the worst treat ever.
• I Lied: Despite making a deal, Skarr happily betrays Bun-Bun at the first opportunity.
• I Need to Go Iron My Dog: When trying to get away from the other members of Underfist, Skarr pulls this:
  Skarr: Uh, I have to go wash my hair. [Maniacal laughter].
• Ineffectual Loner: Hoss insists on working alone, as he doesn't trust monsters or Skarr. He repeatedly gets overwhelmed by superior numbers.
• Jerkass Has a Point:
  • Skarr angrily tells Jeff and Fred to grow up, saying they have to take stock of how monsters are taking over the world. Fred says Skarr is mean, but Jeff concedes he's still got a point.
  • Critical as ever, Dracula tells Irwin that he has to accept who he is and that only he can decide what he wants to be in life.
• Last-Second Joke Problem: An army of squid warriors crash the award ceremony for Underfist at the end of the special, as the team gets ready to fight them.
• Little "No": Hoss, upon realizing he has encountered Bun-Bun before.
• Little Useless Gun: Parodied. The candy soldiers wield rifles that fire soda that, at most, will give someone sticky clothes and a rash. One soldier questions whose idea this was.
• The Man Behind the Man: Bun-Bun initially appears to be leader of the chocolate bar soldiers, but he is later revealed to be The Dragon to Mindy. However, he is actually the true mastermind, and he was only using Mindy to get to Irwin.
• Medals for Everyone: After Underfist has saved the world, President Mandy gives each member of the team a gold medal, though Skarr’s medal is from a Little Miss Endsville pageant, much to his annoyance.
• Mirror-Cracking Ugly: Mindy, after being transformed into a witch. One smile into a mirror causes it to crack.
• Missing Mom: Parodied when Hoss Delgado lies about his mother having passed away so people won't know he still lives with her at 48 years old.
• Negated Moment of Awesome: Just as Irwin's about to unleash his dark mummy vampire powers he gets run over by Jeff.
• Ninja Pirate Zombie Robot: Irwin is a mummy vampire.
• Non Sequitur, *Thud*: B (Billy), after being thrown against a wall by an invention:
  B: I'll have the fried pickle. *Thud*
• Overly Long Gag:
  • Fred Fredburger spelling his name one letter at a time, intercut with Hoss and Skarr getting their butts kicked by candy soldiers.
  • The Reveal escalates to this. Bun-Bun being the monster that scared Hoss as a child was given legitimate foreshadowing, while him manipulating Mindy is played as a twist. Then he takes credit for making Billy afraid of spiders, thus ruining Jeff's relationship with him, and boasts he sawed off Fred's previously never mentioned tusks.
• Personalized Pledge: Rejecting the team uniform, Hoss vows on his mother's tomb to not work with freaks and monsters. He keeps forgetting that his mother is still alive.
• Pre-Asskicking One-Liner: After the villains openly laugh at Hoss for still living with his mother.
  Mrs. Delgado: You play nice now.
  Hoss: [smirking and cracking his knuckles] Yes, Mommy.
• Pre-Mortem One-Liner: Hoss lets one loose before he fires the Candy Blaster.
• Ragtag Bunch of Misfits: The fate of the world depends on a vampire/mummy hybrid, a one-eyed weirdo with a hatred of monsters, another one-eyed weirdo whose loyalties are questionable, a Giant Spider trying to be more mature, and an excitable Cloudcuckoolander that just wants to play.
• Rapid-Fire "No!": Fred in response to the team splitting up almost immediately.
• The Reveal: Parodied. Bun-Bun was the one truly responsible for Mindy turning into a witch by putting a witch worm in her hair. And he was the monster who scared Hoss when he was little and made him wet the bed and hate monsters. And he made Billy (Jeff's father) afraid of spiders. And he sawed off Fred Fredburger's tusks.
• Rewind Gag: Near the start of the special, a Fake-Out Fade-Out starts after Irwin gives up on his evening, complete with fake credits. As soon as Mindy reveals that she wants Irwin's help, the credits rewind back to Irwin.
• Samus Is a Girl: The new president is revealed to be Mandy.
• Self-Deprecation:
  • When Jeff mentions the idea of "working a job that I hate" it cuts to him being a cartoonist. Bear in mind that he's voiced by series creator Maxwell Atoms.
  • Halfway in, Irwin questions why a marshmallow bunny (something typically associated with Easter) is even in a Halloween Special in the first place.
• Shout-Out:
  • Irwin says "Like sands through the hourglass, so are the Days of Our Lives."
  • Early on, Skarr dons a robot suit similar to the one Ellen Ripley wears in Aliens.
    Skarr: Get away from my garden, you rich dark chocolates!
  • He also later dresses up like Freddy Krueger.
  • Mindy at one point wears a costume that looks heavily similar to The Evil Queen from Snow White and the Seven Dwarfs.
  • At one point, Mandy displays the Confectionomicon, which is designed as a candy-themed parody of the Necronomicon from Evil Dead.
  • Billy as B is dressed like Dexter of Dexter's Laboratory.
  • The villains attempt to kill Hoss by pushing him off a skiff à la Return of the Jedi, complete with Hoss calling Mindy a "slimy, worm-ridden piece of filth".
• Spin-Off Babies: Parodied with Underfist Babies in the ending credits.
• Temporary Bulk Change: Once Billy eats the giant chocolate bar mummy monster, he is left stuffed and round like a beach ball.
• Tempting Fate: Nergal enjoys the family picnic, saying he's never been happier. Sis lampshades the trope right before Jeff crashes the truck right through the dome, causing lava to pour in.
• The Stinger: Billy says "All that work and nothing to show for it!" after the end credits are over.
• Understatement: Irwin trying to comfort Fred:
  Irwin: Yeah, it's been a pretty whack Halloween, yo.
• Victory by Immodesty: When Endsville first gets invaded by candy soldiets, they spray Hoss with grape soda. Hoss is obviously unharmed, but he complains that they made his clothes sticky and gross, so now he’ll have to fight naked. He then rips open his shirt, revealing his extremely hairy chest. The candy soldiers are so disgusted by the thought of seeing him naked that they immediately retreat.
• Villain Song: Mindy sings "Trick-or-Treater Eaters" when she whips up the brew needed to make the candy monsters stronger.
• Wimp Fight: Hoss and Irwin finish their brawl by feebly slapping at each other.