The Simpsons' 12th season began on Wednesday, November 1, 2000 with "Treehouse of Horror XI". The season contains three hold over episodes from the season 11 production line. The show runner for the twelfth production was Mike Scully. The season features three episodes that were produced for the eleventh season which was also run by Scully. The season won and was nominated for numerous awards including two Primetime Emmy Awards wins and an Annie Award.
This year's Halloween story sees The Simpsons as "The Munsters" (with everyone except Lisa getting killed), Homer as a wandering spirit on the hunt for a good deed in "G-G-Ghost D-D-Dad," Bart and Lisa as peasants in a fairy tale forest in "Scary Tales Can Come True," and Lisa inadvertently dooming mankind by rescuing a dolphin in "Night of the Dolphin."
While calling Animal Control over a badger taking residence in Santa's Little Helper's doghouse, Homer discovers that Springfield has two different area codes–and ends up leading a revolt that splits the town in two.
Krusty takes parenting lessons from Homer when, during an outdoor book fair, a girl tells Krusty that she is his long-lost daughter from a one-night stand with a female soldier who fought during the first Gulf War.
Lisa falls for the teenaged leader of a militant environmentalist group and tries to impress him by living in Springfield's oldest tree in order to keep it from being cut down.
When the Simpsons once again have financial problems, Mr. Burns pays Homer to play pranks on others and humiliate himself in public. Meanwhile, Smithers creates a Malibu Stacy-themed musical.
Homer decides to buy a computer after turning up to the Plant to find it closed by e-mail. He then creates his own website and it eventually gains attention when he posts gossip. Homer dubs himself as "Mr. X" to conceal his identity. When he reveals that he is Mr. X, he becomes drugged into a mysterious island where people who know too much are imprisoned after Homer starts writing conspiracy theories such as flu shots.
Homer and Bart become father–son con artists (after Bart is given money out of pity when Homer decided to not take him home), but soon find that they are the ones being had.
A snowstorm traps the students of Springfield Elementary inside, with them overthrowing Principal Skinner when he uses his Army skills to control them. Meanwhile, Homer tries to rescue the children–using Flanders' car.
While working as a human guinea pig (to pay off the family's lost savings after making a bad investment), Homer discovers the root cause of his subnormal intelligence: a crayon that was lodged in his brain ever since he was a boy. He decides to have it removed to increase his IQ, but discovers that being smart does not necessarily equal being happy.
Marge tries to rehabilitate a convict with remarkable artistic talent. Meanwhile, Homer uses a trash can to fix people's spines.
Bart and Milhouse are banned from The Android Dungeon after stopping Comic Book Guy from buying a box of priceless Star Wars memorabilia for $5, but are hired as his replacements when Comic Book Guy has a heart attack and is advised to leave his job in order to make friends.
While making funeral arrangements for Grampa's future, the funeral planner pitches the idea of a mausoleum that uses the same amount of cement as a full-sized tennis court. This prompts Homer to instead build a tennis court in his backyard, initially mistaking the sport for "Foxy Boxing". The tennis court makes Marge and Homer popular in town, but it turns out that this is only because Homer's inferior tennis ability makes them an easy target. Bart on the other hand, shines as a natural.
Krusty announces his retirement due to interference from network executives and the growing popularity of the big-money game show "Me Wantee", but when Krusty reveals to Sideshow Bob that all of the episodes featuring him have been erased, Sideshow Bob uses Krusty's biggest fan (Bart) to murder him during Krusty's farewell show.
A music producer selects Bart, Nelson, Milhouse and Ralph to be members of the next hit boy band, who record subliminal songs about joining the Navy.
Homer becomes a Good Samaritan after discovering the simple joys of helping people in need–which is put to the test when he goes on a hunger strike after the owner of the Springfield Isotopes attempts to discredit him when Homer stumbles on his plot to discreetly move the team to Albuquerque, New Mexico.
When Lisa becomes the target of a female bully, Lisa discovers a scientific reason as to why bullies pick on nerds. Meanwhile, Homer goes into the baby-proofing business, which is threatening the businesses of pediatricians and greeting card salesmen.
When the Simpsons run out of food thanks to a bag boy strike (caused by Homer), the family finds an old box of animal crackers with a sweepstakes that sends The Simpsons to Africa.
Homer's rush to the hospital to reattach his thumb, Lisa's rush to school to win the science fair, and Bart's run-in with an illegal fireworks scheme are interconnected in a parody of Go and Run Lola Run.
After finding a sketchbook belonging to his late wife Maude, Ned Flanders opens a Bible-themed amusement park to honor her memory.
After spraining his knee during a basketball game, Homer begins taking care of the neighborhood kids to cure his boredom, prompting jealousy from Bart and Lisa, who feel that Homer is giving the kids the attention they never had.
When Homer refuses to pay a five dollar airport tax to fly to Delaware, the family is forced to ride in a livestock car of a train instead. There they meet a singing hobo who tells three tall tales: Homer as Paul Bunyan. Lisa as Connie Appleseed, a parody of Johnny Appleseed. Bart as Tom Sawyer with Nelson as Huckleberry Finn.