|Wrath of the Spider Queen|
Billy & Mandy's Big Boogey Adventure
Underfist: Halloween Bash
- Written by: Maxwell Atoms
- Storyboard by: Clayton Morrow & Alex Almaguer & Mike Diederich & Chris Headrick
- Art direction: Marc Perry
- Directed by: Kris Sherwood & Matt Engstrom & Gordon Kent & Juli Hashiguchi
When Grim’s past comes back to haunt him, Billy and Mandy must join forces with their greatest enemies respectively to save the day from evil spiders trying to take over the whole world. And to do that, Billy must conquer his fear of spiders
In Ms. Butterbean's class, everybody begins to notice that spiders are appearing everywhere, and students keep disappearing, being attacked by giant spiders while in the halls. Later, in the cafeteria (which is also filled with spiders), Billy leaves the table to get some milk, and finds two, one regular and one chocolate, each with a talking cow's head on it. He takes the chocolate milk, but before he can return to his table, is he abducted by Jeff, and brought into the school's walls and air vents; in the process Billy drops the milk, which Jeff picks up. Jeff tells Billy that he is getting married, and wants Billy to come to the wedding. He then leaves in a hypnotized-like trance as he hears a strange song; Billy, afraid of Jeff but wanting his milk back, follows. There he meets Velma Green, Queen of the Spiders and Jeff's fiance who has assembled an army of spiders and has allied with the Dark Elves.
Billy and Jeff both leave Velma's presence to go to the Spider Palace, where Velma will meet Jeff for the wedding. On the way, Jeff accidentally drops the milk, spilling it. The cow on the box talks to Billy again, telling him that it was Jeff's fault; and out of rage and sorrow for his lost milk, Billy screams at Jeff that he wants nothing to do with him or his "hairy girlfriend." Jeff then suddenly erupts in a fit of rage, and screams that he wants nothing to do with Billy for all his horrible parenting over the years, and he leaves. Billy, somewhat sadly, drinks the rest of his milk, only to realize that it's more than thirty years past its expiration date.
Meanwhile, Velma attacks the school, and kidnaps Grim, Mandy and Mindy, as well as everyone else in her cocoons of spider web.
As Grim explains, Velma and he were friends thousands of years ago (130,000 to be exact) in junior high school, but that she was supposed to have been elected Reaper, and when he was she swore revenge. Velma, for her part, claims that Grim had cheated. Velma plans to eat Grim's head, thus giving herself all of his powers; when she starts, she opens a hole in his head and is able to see his memories, initially viewing a Betty Boop cartoon by complete accident, and being warned by Grim that there are parts of his mind she shouldn't view. She orders that they be shown on a large screen for everyone to see, so that all would know the way he cheated her.
In Grim's memory, he and Velma became friends when they first met; their mutual enemy was the Boogeyman. When the position of Reaper came about, all three ran in a school election to choose who would get it, with Velma being the front-runner (note that this contradicts with previous episodes, where Grim either became Reaper as a child or took on the position after his father). When a little less than half the votes had been cast, Boogey destroyed them and attempted to stuff the ballot box with votes for himself, only to be stopped by Grim. Then, feeling that Velma deserved to win, Grim stuffed the box with votes for her, but she caught him and ran off crying, thinking he was trying to cheat for himself.
In the present, while Velma and everyone else is watching Grim's memories, Mindy and Mandy have broken out of their prisons and are attacking the spiders and Velma's other servants. Velma and Jeff get into a fight (spanning an entire commercial break), with Jeff still raging not only about Billy, but also about Velma and how she folds his shirts wrong. Meanwhile, Billy has sneaked into the school for more milk, only to encounter the talking non-chocolate milk, which tells him to release his anger.
After this, Mandy returns to Grim's body and asks it where the head is. The body points to the sky and Mandy sees Velma with Grim's head climbing to the top of the Spider Palace. Mandy follows her to the top but before she can do anything Mindy notices Billy with an army of Eagles. All the Eagles are caught in the spiders webs but Billy manages to escape. He then flies over to Velma with two large Eagle feathers and knocks Grim's head from her hands. After Mandy catches it she jumps back down to the ground. An enraged Velma follows her and before she can attack Mandy, Mandy tells her to look inside Grim's head one last time. When she does, she sees Grim cheating again but then sees that Grim was stuffing the box with votes for Velma.
After Velma had run off crying,Grim had hunted down Boogey, angry at him for everything, and attacked him with the prototype Scythe reserved for the winner of the election. Everyone who hadn't voted was so impressed that they all voted for him, and thus he managed to win despite having cheated for Velma. Velma talks to Grim and Grim tells her that he thought she should've won. Velma then apologizes to Grim and their friendship is reconciled.
Billy arrives with the others, and tells Jeff that he is not really angry with Billy or Velma, but must release the "spirit of anger" inside him. Suddenly, out of Jeff's mouth emerges a half-cow, half-spider creature called Arachnotaur, who claims to be the god of anger from Velma's home galaxy. He explains that he had been trapped by the celestial beings inside a milk carton for decades, but that he had manipulated Billy to become free and then possessed Jeff. Billy allows Arachnatar to beat him up until he gets bored and walks away. Jeff returns to his normal, loving self, and he and Billy reconcile.
Everything ends well, and Jeff and Velma are married, though immediately afterwards, Billy declares that his son isn't going to marry a spider (despite the fact that Jeff is a spider, too), so Jeff cancels the marriage. Velma is not too upset, and since her plans for becoming the Reaper did not go through and just attempt to pull out plans to conquer the world like her dad wanted. She sings her strange song again, and spiders begin attacking Endsville.
- At the beginning of the movie, Billy summons Grim to "show and tell" in his class, but Ms. Butterbean points out that while it cool at first, at this point in the series, the "magic has gone away." Grim himself even points out that Billy brings him to school so much that he probably knows more about certain subjects than Billy does (like the metric system).
- While Grim isn't always seen at school with Billy and/or Mandy, he does go to school with them quite often.
- The scene where Billy tells Jeff to leave resembles the scene from Star Wars Episode VI: Return of the Jedi where Darth Vader redeems himself to Luke before his death.
- When Velma first looks inside Grim's memory, footage of a black and white Betty Boop cartoon was shown.
- Jeff claimed that Billy never let him see Mom in this film, even though Billy never married. Billy however almost married Mandy and an underworld girl.
- This is the only time Billy is able to communicate bravely towards Jeff for a while.
- The chocolate-milk carton was passed the expiration date in 1974.
- The entire film's plot-focus is a spoof of the 1987 film Arachnaphobia and the 2002 film Eight-Legged Freaks.
- During the end credits of Underfist, there is a title card for a (fictive) sequel called "Underfist: Return of the Spider Queen".
- This is the first time dinosaurs were depicted. The second is the title card displayed during the end credits of Underfist: Halloween Bash called Underfist Vs. The Dinosaurs.
- This is the only film in the franchise without Fred Fredburger.
- Cartoon Network USA aired the movie in HD for the first time on October 8, 2017.