This Halloween-themed episode consists of a trilogy of strange tales:
Ducky Momo Turns Evil: Candace accidentally conjures up a spell that turns her Ducky Momo plushie into a living, breathing doll that is set on stalking her.
Night of the Giant Floating Baby Head: Doofenshmirtz encounters the inexplicable Giant Floating Baby Head that grants cursed wishes, which could make him supreme ruler of the Tri-State area, that is, if he says it the right way.
Invasion of the Evil Platypus Clones: Phineas, Ferb and their friends confront a horde of mischievous, evil platypuses set on destroying the town.
When Vanessa learns that her father has inherited a Drusselsteinian castle right next door, she seizes the opportunity to throw the biggest Halloween bash ever. The whole town is there, including Phineas and Ferb, who act as the event's party planners and DJs. Meanwhile, Doofenshmirtz enlists Perry to help him find a large, hidden treasure that his great aunt has placed somewhere within the castle.moreless
After learning about Monty and Vanessa's secret relationship, Carl bribes Monty into helping him get some much needed acknowledgement from Monogram. Meanwhile, Candace is ecstatic when she discovers that her neighbor Peggy McGee has witnessed all of Phineas and Ferb's summer antics and is happy to tell Mom about them. Also, Dr. Doofenshmirtz creates its "Inflator-inator" to try to silence his neighbor who plays the bagpipes every day.moreless
Spider-Man, Iron Man, Thor and Hulk stand powerless after being struck by Dr. Doofenshmirtz's power-draining "inator." Once the Marvel Super Villains - Red Skull, Whiplash, Venom and M.O.D.O.K. - find out that Dr. Doofenshmirtz is responsible for robbing the superheroes of their powers, they seek him out and together create mayhem in Danville. Meanwhile, Phineas and Ferb do everything they can to restore the superheros' powers before the evil villains take over the world.moreless
The boys set out to prove the existence of the elusive Chupacabra to the world, but Candace can't stand the wait and needs to first just prove it to mom. Meanwhile, Doofenshmirtz has the brilliant idea to use his Switch-Place-Inator to remove hair from one person and give it to another so that he can in turn sell his hair growing tonic.moreless
Candace thinks her day will be easy when the boys actually ask her to get Mom if they get stuck in their gigantic reproduction of the Gordian Knot, but when Jeremy stops by and asks for her help to open his personal mini safe, she finds her day getting a little more complicated. Meanwhile, Doofenshmirtz plans to eliminate every all-you-can-eat buffet in the Tri-State Area with his Eat-It-All-Inator.moreless
When Candace thinks Jeremy is bored with their usual hangouts, she sets out to find something unique to do with him. Meanwhile, Phineas and Ferb power through town surfing on a giant ball of water and Doofenshmirtz plans to use his Double-Negative-Inator to confuse his local eatery into giving him a wintery drink that is usually not served during summer.moreless
The boys make a giant inflatable wading pool for Mom. Meanwhile, Candace reveals her "Emo" side, and Doofenshmirtz attempts to become ruler of all bees.
When Perry comes face to face with an Australian platypus hunter named Liam, who is set out on destroying him, his unwavering demeanor is threatened and his life is put in danger -- he must find a way to defeat this villainous foe, rescue Doofenshmirtz from the error of his ways and save himself from the hunt. Meanwhile, Baljeet is having an existential emergency and finds himself incapable of making decisions, so Phineas and Ferb create an infinite probability generator that will allow Baljeet to make as many choices as he pleases without being affected by the consequences.moreless
Agent P teams up with a former partner, a human agent named Lyla, to stop a hijacked train running along the US/Canadian border. In a past mission, they had a falling out, so Agent P must decide whether or not he can trust Lyla and her unique sense of logic to get them through the mission, defeat Doofenshmirtz and save the train's passengers and Canada's national treasure - a moose named Albert.moreless
The boys create Rutabaga-themed vehicles when Candace is chosen to be Rutabaga princess and gets to start the "Running of the Chinchillas." Across town, Doofenshmirtz plans to turn himself into a real live Kinderlumper to scare Roger into relinquishing control of the Tri-State Area over to him.moreless
Candace challenges Buford to keep Phineas and Ferb's invention from disappearing so that she can sweep in and casually bust her brothers. Across town, Doofenshmirtz has had one too many lattes and is experiencing an extra burst of evil energy.moreless
Buford removes a part from a tire swing the boys are building and it accidentally shoots a ray that turns Candace into a fly. Meanwhile, Doofenshmirtz is suffering from evil scientist's block.
National Hockey League star Luc Robitaille offers his assistance when Phineas and Ferb take an ice hockey game to the extreme. Meanwhile, Doofenshmirtz builds an Abominable-inator to make himself bigger, scarier and hairier.moreless
Phineas and Ferb plan their own New Year's Eve ball drop, complete with a customized multidimensional ball, while Candace makes it her resolution to refrain from busting her brothers before the clock hits midnight. Meanwhile, Doofenshmirtz uses a Resolution-Changer-Inator in his tie as he continues the never-ending attempts to take over the Tri-State Area.moreless
Jack tries to avoid his mother. Meanwhile, Jenna starts to envy Liz and her married life.
Candace is put in charge of Phineas and Ferb just before they seize the opportunity to make the most of Danville's electricity blackout while Dr. Doofenshmirtz tries to use pity to his advantage with his latest -inator.moreless
At Stevie's bar mitzvah, friends and family gather and Nancy tries to reconnect with her estranged loved ones.
After discovering that a strange planet is hurtling directly towards Danville, Phineas and Ferb set out to avert a disaster, while Buford looks forward to making contact with its alien race. Meanwhile, Dr. Doofenshmirtz hopes to steal the world's largest ball of twine.moreless
Agent P's fate is finally revealed in the action-packed finale of the two-parter that left Phineas, Ferb and the gang hanging--literally off an unchartered gorge and Candace frantic over a phone call with Jeremy that left their relationship status in limbo. Now, with Agent P nowhere in sight, Dr. Doofenshmirtz and Major Monogram square off against evil Carl, who controls a set of robots resembling Phineas, Ferb, and company, to take over the OWCA, in one of the biggest battles yet.moreless
The Flynn-Fletchers are off on an African safari, leaving Perry at home to deal with Doofenshmirtz and his most evil plot yet; to take over the Organization Without a Cool Acronym. But when Doofenshmirtz accidentally zaps Carl with his Ultimate-Evil-Inator ray, Carl takes over the O.W.C.A. and imprisons Doof and Monogram. Agent P steps in, but gets zapped with Doof's many raysand in the cliffhanger of all cliffhangers, disappears.moreless
Phineas and Ferb are helping their father unearth a missing piece of Danville history when they run into his lifelong nemesis, Worthington Dubois, at a swap meet. Meanwhile, Dr. Doofenshmirtz makes himself younger to win a children's film festival, and Candace uses the swap meet to try and get an extremely rare Ducky MoMo item.moreless
Meap returns to save Phineas and Ferb from his nemesis Mitch, whose real mission is to take control of all of alien-kind, putting Meap's world in danger. The boys' 'cute-tracker' leads the gang to Seattle and an adventure to save the universe. Meanwhile, Dr. Doofenshmirtz decides to revisit his former nemesis, Peter the Panda, but when Agent P shows up, Dr. Doofenshmirtz finds that he has some explaining to do.moreless
After Mom asks the kids to keep quiet while she prepares for her online knitting test, Phineas and Ferb create ninja outfits designed to hide the wearer from anyone who is not wearing them. Meanwhile, Candace becomes increasingly frustrated after she can't find the boys and bust them. Across town, Dr. Doofenshmirtz invents the De-Handsome-Inator, which actually works in his favor as his newfound handsomeness makes him appealing to everyone in the Tri-State areamoreless