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It's Halloween night, and Phineas, Ferb, Candace and their friends visit a haunted house. Meanwhile, Doofenshmirtz's attempt to transfer his mind into a cow to declare war against grass has gone wrong, transforming him into a ferocious werecow Perry needs to keep from wreaking havoc.

!!Tropes
* AgentScully: Baljeet refuses to believe in the existence of ghosts.
-->'''Buford''': Whatta ''you'' know? You're a daffodil!\\
'''Baljeet''': [[InsistentTerminology Daisy!]]\\
'''Buford''': Case closed!
* AllJustAPrank: It’s revealed that Russell’s home was never really haunted or filled with monsters, it was just some good old-fashioned HalloweenTrickery put on by his parents.
* AllPartOfTheShow: When Doofenshmirtz in his were-cow form rips through the backdrop of a little kids’ farm play, the audience thinks it’s part of the show and applauds.
* BalloonBelly: After turning back into a human, Doofenshmirtz has one from gorging himself on grass as a were-cow.
* BedsheetGhost: While in the CreepyCemetery that’s inexplicable in Russell’s basement, a ghost can be heard describing herself as such and a clothesline with a ghost-shaped sheet flies past.
-->'''Ghost:''' I’m not a ghost...I’m a sheet...that lives!
* BehindAStick: Parodied. Were-Cow!Doofenshmirtz hides behind a lamppost and is clearly visible, but the angry mob completely misses him.
-->'''Mob Member:''' He could be hiding behind any one of these poles!
* BorrowedCatchphrase: Baljeet borrows Phineas’ OncePerEpisode catchphrase, “Hey, where is Perry?”
* BrainFood: Like all good zombies, the ones in Russell’s basement are hungry for brains...and spleens and pancreases and kidneys.
-->'''"Proper" Zombie''': I don't care for organs, but I do enjoy a cucumber sandwich. (gets trampled) Dash it all, they broke my saucer.
* BrickJoke: The couple at the house Candace trick-or-treats at with Phineas and Ferb thinks she’s not wearing a costume. Later, when they meet up with the rest of the kids, Buford also asks her why she’s not dressed up.
-->'''Candace:''' Where’s your costume?! I haven’t worn my hair like [[GirlishPigtails this]] in two years!
* CarnivoreConfusion: Played with. During his chase scene with Perry, Were-Cow!Doofenshmirtz makes a beeline for the refrigerated section of a grocery store and chugs a carton of milk.
* ContinuityNod: This wasn't the first time Carl pretended to be Monogram.
* CreepyBasement: Russell’s basement, to say the very least. It features a cemetery, ghosts, a river (possibly made of blood), and zombies.
-->'''Buford:''' I gotta say, this is a really nontraditional use of interior space.
* CropCircles: Doofenshmirtz as a were-cow makes a crop circle in the shape of a cow.
* ForHalloweenIAmGoingAsMyself: Candace is supposed to be dressed as Literature/{{Heidi}}, but one of the neighbors, who hasn't seen her in a long time, assumes this is what she is doing. Also, Isabella tries to claim this, before sheepishly admitting that she got her costume from the Googolplex Mall.
* ForcedTransformation: As a result of an experiment gone wrong, Doofenshmirtz transforms into a were-cow, and a [[AnimalGenderBender bull with udders]] at that.
* FunnyBackgroundEvent: During the chase scene, one of the mob members takes a water cup and sips it as if he is running a race.
* GhostButler: Immediately after the group enters Russell’s house, the wind blows out the candles lighting the room and the front door slams behind them.
* HalloweenCostumeCharacterization: TheBully, rough and tumble Buford, goes as a {{Pirate}} for Halloween. Baljeet however, who’s weaker and more InTouchWithHisFeminineSide, dresses as a daisy.
* HalloweenEpisode: The third, and the first to actually take place on Halloween.
* HauntedHouse: The kids meet a boy named Russell who lives in one of the OldDarkHouse variety and they decide to help him rid his house of the ghosts that are terrifying him.
* TheIgor: Perry dresses as this when trick-or-treating with the gang.
* InsistentTerminology: Baljeet is not dressing as a daffodil, he's a daisy.
* LettingTheAirOutOfTheBand: Angelic harp music plays when Isabella jokingly says she’s not wearing a fairy princess costume. When it goes right over Phineas’ head, the music dies down as Isabella admits she got her costume at the Googolplex Mall.
* LiteralMetaphor: Doofenshmirtz uses one of his inventions to literally give a cow “a piece of his mind” by transferring some of his thoughts into the cow’s head.
* NoodleIncident: Doofenshmirtz, for reasons he refuses to explain, declared war on grass. He claims the reason is unimportant.
* OurWerebeastsAreDifferent: Due to an inator gone wrong, Doof is cursed to transform into a werecow, which is as ridiculous as it sounds.
* PainfulTransformation: Doof transforming into a werecow.
* PumpkinPerson: A monster with a jack-o-lantern for a head appears and says the OncePerEpisode, “Aren’t you a little young to be...” line.
-->'''Jack-O-Lantern Monster:''' Aren’t you a little young to be hunting ghosts?
-->'''The Gang''': ''(frightened)'' Yes! Yes, we are!
* PunnyName: The little boy is named Russell (rustle), and his parents are Waylon (wailin') and Mona (moanin'). {{Lampshaded}} twice by Isabella.
-->'''Isabella:''' Oh Russell! Like the leaves.
* RealAfterAll: Subverted. Phineas mentions how he almost believed the haunted house was real and then looks back to see that the house has disappeared. It turns out it was just an inflatable house and Russell’s family was packing it up for the night.
-->'''Phineas:''' Isn’t this the moment in one of these things when someone ''really'' turns into a ghost?
-->''({{Beat}})''
-->'''Russel''': Dude, that's it!
* RoboticReveal: The Jack-O-Lantern Ghost is revealed to be a robot after Ferb knocks its head off.
* ScaryFlashlightFace: Russell does this while telling the other kids about his haunted house. Also Baljeet when asking the inevitable question.
-->'''Buford:''' The light under his chin makes his story pretty convincing.
* ShoutOut:
** When the kids enter the haunted house, music similar to the theme from ''Franchise/{{Halloween}}'' plays in the background.
** The devices used by the kids to investigate the house closely resemble the PKE Meters used in ''[[Film/Ghostbusters1984 Ghostbusters]]''.
** Doofenshmirtz uses a mind transmitter on a cow and turns into a Were-Cow, similar to how Wallace in ''[[WesternAnimation/TheCurseOfTheWereRabbit Wallace & Gromit: The Curse of the Were-Rabbit]]'' used one on the rabbits and turned into the Were-Rabbit. Also, in the Book of Monsters, the page before Were-Rabbit is Were-Cow.
* SpecialEditionTitle: Only the very last part of the title sequence is different, with spooky music and Halloween-themed scenes from "[[Recap/PhineasAndFerbOneGoodScareOughtToDoIt One Good Scare Ought to Do It!]]" and "[[Recap/PhineasAndFerbTheMonsterOfPhineasNFerbenstein The Monster of Phineas-N-Ferbenstein]]" as well as concept art from "[[Recap/PhineasAndFerbAreYouMyMummy Are You My Mummy?]]" (with Phineas having his original red and yellow striped shirt, green pants, and red shoes and Candace in her original green dress) in the background.
-->'''Candace:''' Mo-om! Phineas and Ferb are making a Halloween special!
* SpecialGuest: Creator/MichaelDouglas as Waylon and his real-life son, Dylan, as Russell. Interestingly, Waylon's wife is ''not'' played by Creator/CatherineZetaJones to make it a full family affair, but instead by Creator/AprilWinchell.
* TemptingFate: Baljeet asks how the situation could possibly get worse, and Russel says that the floor sometimes gives out. Immediately after, that exact thing happens.
* ThingOMatic: The Mind-Transferinator, which was supposed to allow Doofenshmirtz to transfer a portion of his mind into the head of a cow, but instead turned him into a were-cow.
* TorchesAndPitchforks: After watching a news report about the were-cow, a couple decides to form an angry mob to hunt it town while [[LampshadeHanging lampshading]] the fact that they coincidentally already had a torch and pitchfork with them.
-->'''Woman:''' Wait a minute. You brought a ''torch'' on our date?
-->'''Man:''' Hello?? Pitchfork?!
* TooOldToTrickOrTreat: Candace is only trick-or-treating with her brothers until she can get to Jeremy’s house, because she thinks she’s too old to spend the whole night doing so.
* WhatHappenedToTheMouse: It is never shown what happened to Doofenshmirtz after he becomes a werecow, and chased by the mobs and Perry. However, knowing how Perry is always one step ahead and due that the next episodes always have Doofenshmirtz back to normal, it could be assumed that Perry manage to capture the mutated Doofenshmirtz and help him to cure his mutation.
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