!I Know What You Diddly-Iddly-Did

The Simpsons are driving on a foggy night, and since Homer forgot to put the fog lights on, Marge pulls over to be safe. She ends up hitting Ned Flanders. No one else is there, but when they're returning from Flanders' funeral, they find that someone has painted 'I know what you did' on their door, freaking the family out, since it means that someone saw them kill Flanders.

That night, while the family is sitting at the couch during a thunderstorm, the phone rings ominously. Homer picks it up, and the voice at the other end says "I know you're alone". But wait, Homer's not alone. The voice asks if it's Maude Flanders, and on being told that he's speaking to Homer Simpson, apologizes. Turns out, it's Moe, and he had the wrong number. Then, a flash of lightning illuminates the room- and reveals that 'I know what you did' has been written all over the walls.

The family sees a dark figure in a raincoat, carrying a hook. They run away, but the car has also been covered with 'I know what you did'. They drive away, and Homer pleads with God to save his life. Right then, the car runs out of gas, and the raincoated figure is right behind them. Homer directs the family to hiding places (the abandoned amusement park, the pet cemetery, the spooky roller disco, the lake where the sexy teens were killed a hundred years ago tonight), but before they can, the raincoat-wearing person catches up to them. Turns out, it's Flanders.

Marge says that it's impossible for him to be alive, since she killed him, but Flanders says that they can't kill the undead. Turns out, he was attacked by a werewolf just before she hit him. Also, the moon is full tonight. The family runs away, leaving Homer behind to be attacked by Werewolf!Flanders.

! Desperately Xeeking Xena

This short opens while the police are x-raying candy to see if it's safe (and some of it isn't- one kid's bag has a hidden razor blade and syringe). One kid tries to force a large bag of candy through the machine, resulting in it breaking and spewing beams of radiation around the room. Lisa and Bart are hit by one, which throws them against a wall, and a set of bleachers falls on Lisa. Principal Skinner is horrified that she's been crushed- now what will happen to their mathletics team?

But then she gets up, holding the bleachers over her head. She then throws them through the roof and into the sky. The X-Rays gave her SuperStrength. Bart wonders if he got powers, and stretches his eyeballs to look around himself. At first he thinks he didn't, before he catches on to what he's doing. Bart realizes that he has stretching powers, and proclaims that he must "only use this power to annoy". He then proceeds to use it to mess with Principal Skinner. Lisa tells Bart that with their powers, they can become superheros. And, as Stretch Dude and Clobber Girl, that is exactly what they do.

Later, Lucy Lawless is answering questions about ''Series/XenaWarriorPrincess'' while dressed as the titular character, when she is abducted by the Collector (Comic Book Guy), who puts her in a mylar bag and plans to marry her. Stretch Dude and Clobber Girl run to the rescue, but are defeated by the Collector, and put into a DeathTrap. In the meantime, Lucy Lawless tricks the Collector, knocks him into his own death trap, and saves the superheroes. She then flies off into the sunset with them. Clobber Girl protests that Xena can't fly, to which Lucy replies that [[IAmNotSpock she's not Xena]], she's Lucy Lawless.

! Life's a Glitch, Then You Die

It's near midnight on December 31, 1999, and Springfield anxiously awaits the new millennium. However, Homer forgets to update his work computer, leading to the Y2K bug running rampant. Everything with a computer chip (including a carton of milk) fails, and cue ApocalypseAnarchy. While the family are walking through Springfield, they see a rocket, which will be used to send the best and brightest of humanity to start a new civilization on Mars. Lisa is allowed on, but she can only choose one of her parents. She immediately chooses her mother, and Lisa, Marge, and Maggie get on the rocket.

Homer and Bart are upset about being left behind, but then they see another rocket, this one unguarded. They get on and the rocket blasts off, but while they're on it, they realize that the rest of the passengers are various washed-up celebrities. And then only Lisa's rocket goes towards Mars- the rocket Bart and Homer are on is headed for the sun. As the celebrities start up a musical number, Bart reassures his father that at least they'll be dead in 5 minutes. Homer says "Not fast enough!" and ejects them both into space, where they smile with relief as their heads swell up and pop offscreen.

Airing on Halloween Night itself (one of only two Treehouse of Horror episodes to do so), it was notably the last annual Treehouse of Horror special to consecutively air in October, something which would not happen again for another full decade.

!!"[=Tropehouse=] Of Horror X":

* AdamWesting: Tom Arnold, who admits he's a lousy celebrity.
* ArtisticLicenseAstronomy: After realizing that he and Bart are being sent into the sun:
-->'''Homer:''' The sun?! But that's the hottest place on Earth!
* BreatherEpisode: "Desperately Xeeking Xena" is a light-hearted superhero parody sandwiched between the traditionally spooky " I Know What You Diddily-Iddily-Did" and the pessimistic BlackComedy of "Life's a Glitch, Then You Die".
* TheCollector: Comic Book Guy's [[CollectorOfTheStrange collection]] includes mylar-wrapped nerd celebrities (such as Tom Baker), the only working phaser ever built, and a functional ''double-lightsaber''.
* ComicallyMissingThePoint: Lisa attempting to be sarcastic to Homer.
--> '''Lisa:''' Well, look at the wonders of the Computer Age now.\\
'''Homer:''' [[SarcasmBlind Wonders, Lisa? Or blunders?]]\\
'''Lisa:''' I think that was implied by what I said.\\
'''Homer:''' Implied, Lisa? Or 'implode'?\\
'''Lisa:''' Mom, make him stop!
* ContinuityNod: During the opening sequence, all the Simpsons are dressed as various creatures they've been turned into during several past Treehouse episodes.
* DamselOutOfDistress: Lucy Lawless.
* TooDumbToLive: Homer in "I know What You Diddily-Iddly-Did" provides the page quote.
* IAmNotSpock: Invoked in "Desperately Xeeking Xena": She's not [[Series/XenaWarriorPrincess Xena]], she's Lucy Lawless. [[MindScrew Despite dressing like Xena anyway.]]
* KilledOffscreen: Unusually, it's Homer who was killed offscreen by a werewolf Flanders eating him.
** Also in "Life's a Glitch," Homer and Bart eject themselves into space, where they inflate like balloons and then pop just off-screen.
* NoahsStoryArc: In the episode spoofing Y2K, after Homer's blunder destroys all electronics on Earth the US government sends two rockets off: one with the best of the best (Lisa is invited) and one which Homer & Bart sneak on to which is aimed directly at the sun.
* NotSoAboveItAll: Marge allows Homer to go looting when he promises to loot her a present.
* OfCorpseHesAlive: The scene from "I Know What You Diddily-Iddily-Did" with Homer fooling Maude into thinking Ned's still alive is even the trope's image source.
* OhCrap: Oh no, Rosie O'Donnell!
* OminousFog
* SadisticChoice: When the world ended, there was a rocket sending the smartest people to Mars. Lisa got to go but wouldn't be allowed to take both of her parents. [[SubvertedTrope She quickly chose her mother as soon as the soldier mentioned the restriction]].
--> '''Homer:''' Goodbye, Lisa. Remember me as I am -- [[TranquilFury filled with murderous rage]].
* ScrewThisImOuttaHere: In "Life's a Glitch", Bart informs Homer that, even though they might be on a rocket with Rosie O'Donnell and Pauly Shore, amongst others, they will be dead in 5 minutes (as they will crash into the sun). Homer is quick to react to this news.
''(Presses button and ejects himself and Bart into space)''
* ShoutOut:
** To ''Film/IKnowWhatYouDidLastSummer'' - though with no explanation as to why Flanders is wearing the slicker and carrying a fish hook.
** The various celebrities and props the Collector is hoarding.
** Marge mentions that the kids are [[Franchise/{{Superman}} vulnerable to Kryptonite]].
-->'''Homer:''' Geez, Marge, tell the neighbourhood!
* SkewedPriorities: Lucy Lawless would rather get captured and forced to marry a super villain than bare her breasts to a crowd of Xena fans.
* SuperheroEpisode: [[RubberMan Stretch Dude]] and [[SuperStrength Clobber Girl]] protect Lucy Lawless from The Collector.
* TakeThat:
** The rocket sent on a collision course to the sun with the apparent purpose of getting rid of the worst/most useless people on Earth, which include such celebrities/familiar 1990s faces as Ross Perot, UsefulNotes/DanQuayle, Tonya Harding, Al Sharpton, Music/CourtneyLove, Creator/SpikeLee, Tom Arnold, Pauly Shore, Rosie O'Donnell and Dr. Laura Schlessinger.
** The Comic Book Guy saying that he fell for a ruse "So hackneyed, it would make Stan Lee blush!" He also notes that his phaser has only been fired once, to prevent William Shatner from making another album.
* TotallyNotAWerewolf: Ned Flanders!
* AWizardDidIt: This episode is the [[TropeNamers Trope Namer]], which comes from a line from Creator/LucyLawless (the actress who plays the titular character of ''Series/XenaWarriorPrincess'') as a quick way to answer fans complicated questions.
--> '''Professor Frink:''' ''(after Lucy Lawless established the phrase)'' But in episode [=AG4=] --\\
'''Lucy Lawless:''' Wizard.\\
'''Professor Frink:''' Aw, for glaven out loud...
* YourHeadAsplode: In "Life's a Glitch, Then You Die", Homer and Bart realize they're on a rocket that's heading into the sun with various washed-up and overall terrible celebrities. Rather than spend another five minutes with Rosie O'Donnell and Tom Arnold, they eject themselves into space, where their heads swell up as they give a blissful sigh of relief and then pop offscreen.