The episode starts with Goddard making a pumpkin Jack-o-Lantern and then Sheen asks what they will be for Halloween. Carl says he is going to be Llama Boy and says this year he is going to wear a cape to make it scary. Jimmy says Sheen is going to be Ultra Lord, again but Sheen says he wore out his costume. The three of them go into the house while Hugh is watching his favorite monster movie "Octopus Man". Carl asks what Jimmy will be this year. He replies that he will not trick or treat, then he makes a deal that he will make Carl and Sheen into monsters, if they give half of their candy.
They go to Jimmy's lab where Jimmy presents his Neutronic monster maker. Carl chooses to be a vampire, and Sheen chooses to be a werewolf. Jimmy turns them into monsters and they go to trick or treat. When Carl cuts himself in the finger with a wrapper, he drinks the blood from his finger and he says he wants more blood. He turns into a bat and flies off. Then Sheen sees the full moon and tries to attack Jimmy. Jimmy panics and immediately flies off with Goddard in the hovercar.
Meanwhile, Hugh accidentally falls into Jimmy's lab and accidentally turns himself into Frankenstein. Judy thinks he made himself a wonderful costume. He tries to grab Mrs. Neutron but she goes to take her costume and gives Hugh a lighter. He quickly throws it out the door. Jimmy then tells Goddard to give him all the information about vampires. Miss Fowl then appears telling him about werewolves because she was married to one. She quickly disappears into fog. Carl finds Cindy, hypnotizes her, and bites her while Sheen finds Libby and bites her. Hugh then goes to the Candy Bar where Sam is playing his violin. Judy then comes and says she needs help at home giving out candy. Hugh does not listen, takes her in his arms, and goes off.
Jimmy then finds Cindy and Carl and finds out Cindy has become a vampire. They transform into bats and chase Jimmy until they suddenly get scared and fly off. Jimmy then realizes that he is standing in front of the display window of Lucky Tony's House of Garlic. He and Goddard go into the alley to sneak back to the hover car where Sheen and Libby sneak up on him. Libby, who has become a werewolf, suggests to Sheen that they should eat Jimmy, claiming that "he said they were going to get something to eat." They chase Jimmy where they also get scared because Jimmy is standing in front of the display window of the Hi Ho Silver Store. Then, Hugh, holding Judy, comes onto the sidewalk, running into Jimmy. Jimmy says that his dad probably went to his lab and turned himself into a monster. The other monsters meet up with the three on the sidewalk. Sheen and Carl attack Hugh while Cindy and Libby are fighting. Judy breaks up the fight by telling them all to work it among themselves. In addition, by work things out, the monsters conclude that they should instead scare other people. Meanwhile, Jimmy goes to his lab and turns himself into a monster, but lowering the settings so that his DNA, unlike the others', will not change.
The monsters go to the Candy Bar where Sam and Miss Fowl call up an angry mob, armed with silver, garlic, and fire. They chase the monsters into the golf course. They all hide from the mob behind the windmill on one of the courses. They then all see Jimmy coming to them from the sky and realize that he turned himself into Octopus Man. He grabs all of them with his arms and takes them home, where he turns them back to normal. They realize that they left their candy behind, and are all very disappointed. Hugh even mentions that no candy on Halloween is scary. Jimmy says that he will fix that, and rings bells with his eight arms. Jimmy in a scary voice says, "Trick-or-Treat". A screen appears showing the words "HAPPY HALLOWEEN".
- Cindy's costume is "Muffy the Vampire Annihilator", which is a parody of Buffy the Vampire Slayer.
- This Halloween episode has the same plot as The Fairly OddParents Halloween episode Scary Godparents where everyone in Retroville become real monsters.
The episode was included on the Jimmy Timmy Power Hour 2 DVD, released by Paramount Home Entertainment in 2006.
|Debi Derryberry||Jimmy Neutron|
|Jeffrey Garcia||Sheen Estevez|
|Rob Paulsen|| Carl Wheezer|
|Mark DeCarlo||Hugh Neutron|
|Carolyn Lawrence||Cindy Vortex|
|Megan Cavanagh||Judy Neutron|
|Andrea Martin||Ms. Fowl|
|Crystal Scales||Libby Folfax|