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.

!!"[=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.
''(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.