[[quoteright:250:http://static.tvtropes.org/pmwiki/pub/images/treehouse_of_horror_x_promo_picture.gif]]
In this year's Halloween special, Marge accidentally kills Ned Flanders, Bart and Lisa become superheroes, and Homer causes a technological apocalypse when his work computer is the only one that isn't [[MillenniumBug [=Y2K=]]]-compliant.

Airing on Halloween Night itself, 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.

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!!"[=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".
* 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.
* IAmNotSpock: Invoked in "Desperately Seeking 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 govenerment 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.
--> "NOT FAST ENOUGH!"\\
''(Presses button and ejects himself and Bart into space)''
* ShoutOut: To ''I Know What You Did Last Summer'' - though with no explanation as to why Flanders is wearing the slicker and carrying a fish hook.
** Marge mentions that the kids are [[{{Superman}} vulnerable to Kryptonite]].
* 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!"
* 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.