In the eighth annual "Treehouse of Horror" episode, Homer discovers that he is the last man left alive after a neutron bomb destroys Springfield in the segment "The HΩmega Man". In "Fly vs. Fly", Homer buys a transporter that Bart uses to switch bodies with a housefly, and "Easy-Bake Coven" features Marge being accused of witchcraft in a Puritan rendition of 1649 Springfield.
A Fox censor, simply named Fox Censor, sitting at his desk reading through the script and deleting scenes, proudly announces that thanks to his editing tonight's Simpsons episode is rated TV-G. But as he says this, a hand with a sword appears out of the on-screen rating icon and stabs him in the back repeatedly. Every time he gets stabbed, the rating gets higher. In the end, the rating is "TV-666" and Censor collapses dead onto the desk. Blood pours down the front to reveal the title, "The Simpsons Halloween Special VIII." Meanwhile, The Simpsons sit on the couch. Metal shackles restrain their wrists and ankles and a metal cap comes down on all of their heads. The family writhes in pain as they get electrocuted.
In a parody of The Ωmega Man,Mayor Quimby generates a great deal of controversy over a "frog's legs" joke he makes about France and he refuses to give an apology. Lisa becomes worried that France will launch an attack against them. Homer tries to reassure her by saying that they have a bomb shelter, but it turns out to be a cardboard box in the backyard. Homer goes to Herman's Military Antiques to look for a real bomb shelter. He is looking at the Withstand-inator when the French president launches a neutron bomb directly into Springfield. Homer, completely unharmed, emerges from the shelter and complains to Herman's corpse about the food. On the way home, Homer does not take notice to the lifeless town. At a green traffic light, he becomes annoyed because the person in front of him will not go. He gets out of his car and chooses to handle matters with a "little friendly punching". He punches the driver in the head, mistaking their head turning into dust for a sign that he 'still has it'. He then notices a newspaper headline that tells about the bomb that blew up Springfield, and he seems to be the only person to have survived. He misses his family, but he quickly gets over his loss and realizes he can do anything he wants. Homer takes this opportunity to watch a David Spade/Chris Farley comedy at the theater and then dance naked in the church, when he is confronted by a group of Springfield citizens including Moe, Ned Flanders, Mr. Burns, Dr. Hibbert, Sideshow Mel, Chief Wiggum, Lenny, Carl, Otto, Principal Skinner, Willie, Apu, Smithers, Barney, Duffman, Lionel Hutz, Professor Frink, Cletus and the Sea Captain all of whom have become mutants(but they prefer to be called either 'freaks' or 'monsters,' as Moe puts it). They claim that they want to create a perfect world in which the mistakes of the past will be eliminated. This, of course, includes killing Homer. Homer flees in a hearse back home with the freaks chasing him in a type of zombie car. Upon arriving home, Homer is greeted by his family, who survived the blast because their house was protected by so many layers of lead paint. Seeing Homer reunited with his family, the freaks see the error of their ways. Ned Flanders hopes they can build a Utopian society where freaks and norms can live together in peace. Marge seems to agree at first, but she and the children (except Maggie) open fire with shotguns that they were hiding behind their backs, killing all of the freaks. Homer and his family plan to take advantage of the nuclear holocaust and go and steal some Ferraris.
In a parody of The Fly and Mad Magazine's Spy vs Spy, Homer buys a teleporter from Professor Frink at his yard sale but refuses to let Bart use it. That night, Bart tries to sneak Snowball II into the teleporter. However, Santa's Little Helper jumps in at the same time. As the pets come out, Santa's Little Helper and Snowball II have been merged into two creatures. Suddenly, a fly lands on Bart's arm, giving him an idea. Hoping to become a fly superhero, he grabs it and steps into the teleporter. Unfortunately, it doesn't work as planned and he and the fly merely end up swapping heads. The rest of the family wakes up and sees Bart's body with a fly's head. The family accepts him as Bart, despite its unusual, non-human behavior.
Meanwhile, Bart regrets his solution and tries to tell his family what happened. However, he is too tiny for them to hear him and is almost killed by the fly-boy that likes its new life. That night, Bart flies into Lisa's room and lands on top of her table lamp which allows her to see the shadow of his head cast upon the wall letting her understand that it is really him. However, she still can't hear him so he flies into her saxophone amplifying his voice enough to tell her what happened. Suddenly, the fly-boy attacks Lisa and starts strangling her. Bart tries to help, only to be caught and eaten by the fly-boy. Lisa knocks him into the teleporter and Bart emerges, now restored back to normal. Homer then grabs an axe, but instead of destroying the machine, he turns to Bart and begins chasing him around for using his teleporter.
In a parody of the 1996 film The Crucible and Easy-Bake oven, which takes place in the year 1649, the town of Sprynge-Fielde is being witnessed because of many witch burnings. Where Chief Wiggum tells the boys to fire up the stake. Then when they are finished burning the stake Nelson Muntz laughs at the notion and Seymour's mother isn't very happy at him which he says goodbye to his mother. Later in the church, the townspeople try to figure out who to condemn next. People begin accusing others and very soon they erupt into chaos, until Marge intervenes. She tries to talk sense into the townspeople, that the witch hunt is turning into a circus but Moe accuses her of being a witch. Mayor Quimby assures her that she is entitled to due process which means she will be thrown off a cliff with a broomstick. If she is a witch she will be able to fly to safety, in which case the authorities expect her to report back for punishment. If she is not a witch, then she will fall to an honorable Christian fate.
Lisa tries to speak on her mother's behalf, but to no avail and Marge gets shoved off the cliff by Wiggum's henchmen. But as Reverend Lovejoy speaks to the mob about having done the Lord's work, they hear a cackle and they all look up, stunned to see that a green-skinned black haired Marge is flying on the broomstick, as she really is a witch and an evil one, who vows revenge on the entire town. At first she turns Chief Wiggum into a gopher with a military hat on his head in revenge for pushing her off the cliff, she turns Lou into a snowman, and Eddie into a fairytale princess. And then eventually Marge tells the rest of them that she will return where her hair pulsates and bursts open sending a swarm of bats flying after the townspeople. Meanwhile, in a cave somewhere, Patty and Selma--who are also witches--are cooking over a black cauldron in their mountain lair close to the village. Then when Marge returns to them she is so sad because the town has forced her to leave her family; however Patty and Selma are glad because of the fact that Marge has "finally left her husband Homer". Later the three over hear Ned Flanders and Maude Flanders talk about how they are worried that the witches might come to normal folks houses and eat children. Soon after, the witches get an idea they go from door to door to eat everyone's kids thus tempting them to hunt in the first place. And so the three set off for Sprynge-Fielde, on their broomsticks, where they then knock on the Flanders's door and demand for their sons. They put the children in sacks and are about to leave, when Maude offers the witches gingerbread men instead. The witches like these better than the children and let Rod and Todd go. They go to each house, getting goodies in exchange for not eating the children. Where the witches compare their treats from a nights work, which they believe that scaring people into giving them treats is fun and that they should do it every year. Marge remarks that she wishes they hadn't eaten so many children before they got to the Flanders' house. But as they fly off the Sea Captain says that is how the tradition of Halloween and trick-or-treating began, with Maude Flanders' fast thinking and leading to Halloween which everyone realizes today.
The next year in the same town, the whole town is celebrating Halloween where everyone is wandering around the streets dressed up in costumes comparing treats, and trick-or-treating. Homer eggs the door of a house from which no candy was received. Lisa points out that Homer is egging their house making everyone laugh. However, when everyone begins laughing at him, Homer then accuses Lisa of being a witch, prompting the townspeople to proceed chasing her down the street into the moonlight.
"The HΩmega Man" was written by Mike Scully, "Fly Vs. Fly" was written by David S. Cohen and was written by Ned Goldreyer. Large portions of the "Fly vs. Fly" segment were cut, including an extended scene with Bart as SuperFly, and the original ending where the fly also emerges from the teleporter, but is considerably larger and the Simpson family ride it to the mall.
The producers had trouble with the censors over several segments in this episode. The opening segment of the episode, which features Fox Censor the censor being stabbed to death and was pitched by David Mirkin, had a difficult time getting through the real life censors. They had issues with the size of the knife and the sound effects used. Originally Fox was stabbed with a dagger, but the censors found it too gruesome, but found the use of a sword acceptable, so it was used instead. The censors also had issues with Homer dancing naked on the altar in the church, so it was changed so that he was just dancing on the floor.
This episode was the only Treehouse of Horror episode that was directed by Mark Kirkland. It was also the last episode that was worked on by Brad Bird, who left the show to direct Warner Brothers' The Iron Giant. "Easy-Bake Coven" was storyboarded by Kirkland and the backgrounds were designed by Lance Wilder. Although Kang and Kodos make brief appearances in every Treehouse of Horror episode, their brief appearance in this one was nearly cut. David X. Cohen managed to persuade the producers to leave the scene in.
The episode received positive reviews from critics and fans. The A.V. Club named Jeffery Albertson's line "Oh, I've wasted my life" as one of the quotes from The Simpsons that can be used in everyday situations.
Homer's line of, "Where did you get those cloaks?", was a result of one of the writers being a big fan of The Omega Man and buying all of the props from the movie, but did not understand where to find the cloaks from the movie.