* AlternateCharacterInterpretation: in spades. The episodes [[InvokedTrope invoke]] this in order to trigger the murders in each segment. See IdiotBall in the main page.
* CrossesTheLineTwice:
** All of Groundskeeper Willie's deaths in "Treehouse of Horror V".
** In "Hell Toupee" from "Treehouse of Horror IX", [[FaceHugger Snake's hair smothers Bart's face]], and Homer immediately begins punching Bart's head.
* EnsembleDarkhorse: Some of the monsters such as Count Burns, Devil Flanders, and King Kong Homer. An unusual example is Krusty in vampire getup from ''Treehouse of Horror IX'' who, despite not really playing a role in the segment, has been seen in TreehouseOfHorror merchandise and media.
** Then you have Kang and Kodos, the two space aliens from the very first Treehouse of Horror segment [[ToServeMan "Hungry Are The Damned"]]. They've appeared in every special since (or not, which they ''will'' unhappily acknowledge) and have even made the odd appearances in the regular episodes.
** The [=THOH=]s themselves might also serve as this. Even people who don't watch the proper episodes of ''The Simpsons'' anymore may tune in [[JustHereForGodzilla just for the specials every year.]]
* FamilyUnfriendlyAesop: Ned teaches one to Bart, Lisa, Milhouse and Nelson about the seven deadly sins in ''Treehouse of Horror XVIII''.
* HarsherInHindsight: ''Treehouse of Horror XIX'' features Homer killing celebrities for commercial rights, among which include Neil Armstrong and Prince. This is hard to watch since both of them are now dead.
* HilariousInHindsight:
** In one episode, Snowball 2 is brought back to life with occult. In a later Franchise/ArchieComics miniseries, Afterlife With Archie, an attempt to bring back Hot Dog starts up the zombie apocalypse.
** In the ''Treehouse of Horror X'' short, 'Life's a Glitch; Then You Die', a virus (in this case, the fabled Y2K Bug) causes chaos around all around the world upon computers, and computer-controlled devices starting from Homer's computer, [[spoiler: leading into the apocalypse.]] Around 10 years later, ''Anime/SummerWars'' would also have it's plot kick off by some guy's computer device accidentally triggering a virus, and causing havoc to devices around the world. [[spoiler: But the big difference here is that Kenji never unleashed it (he just got one letter off, and by being the first to respond, he was framed), it was Wabisuke's doing, and it doesn't end on the apocalypse.]]
* MostWonderfulSound: The familiar ScareChord from the [=THOH=] [[https://youtu.be/I1MLQ2WlAKg promos on Fox]], which have been included in the promos since the early 90s.
* NightmareFuel: Some of the shorts are '''really''' scary such as ''[[ImAHumanitarian Nightmare Cafeteria]]'' and ''[[BlackComedy There's No Business Like Moe's Business]]'' for starters.
** The Gremlin's first appearance in ''Treehouse of Horror IV'' "Nightmare at 5 1/2 Feet" with green fur, a wide SlasherSmile and WideEyesAndShrunkenIrises. The worst part is the ending, where [[spoiler: it reappears on the back of the ambulance carting Bart off to the insane asylum... then holds up ''Ned Flanders' torn-off head'', complete with dangling, gore-slick spinal column, which gurgles Ned's famous greeting to Bart]]. Cue end of the episode.
** ''Treehouse of Horror III'' to ''Treehouse of Horror X'' featured several ''disturbing'' CouchGag sequences, including: the Simpsons family appearing as skeletons[[note]]Treehouse Of Horror III, also used as official promotional artwork for Treehouse Of Horror II[[/note]]; erupting from the ground as zombies[[note]]Treehouse Of Horror IV[[/note]]; mismatched Frankenstein-esque monsters [[note]]Treehouse Of Horror V; this one serves as a SelfParody to another CouchGag where normal Simpson family members have mismatched body parts, but while in that one they correct the mistakes, in this one they screw it up even more[[/note]]; open-eyed hanging victims ([[RefugeInAudacity with Maggie still sucking her pacifier]])[[note]]Treehouse Of Horror VI; this one comes ''right after'' a HeadlessHorseman Krusty throws his own head at the screen, with the resulting blood splatter spelling out the title card[[/note]]; TheGrimReaper sitting on the couch, and the family members dropping dead one after another (and on each other) as they rush to the couch[[note]] Treehouse Of Horror VII; here, after this happens, the reaper [[RefugeInAudacity leans his feet on Homer's corpse]][[/note]]; the family getting electrocuted to death by an [[RefugeInAudacity "electric couch"]][[note]]Treehouse Of Horror VIII[[/note]]; the family ''actually never making it to the living room'' due to [[{{Deconstruction}} screwing up the timing of the opening]][[note]]Treehouse Of Horror IX; it could be argued that Marge and Maggie don't actually die, but even then, they would find [[BolivianArmyEnding Freddy Krueger and Jason Voorhes waiting for them.]][[/note]]; and a GrandFinale of sorts for the couch gags with a ContinuityCavalcade[[note]]Treehouse Of Horror X; said cavalcade consisting of Homer-in-the-box (THOH II), Alien-Maggie (THOH IX), Half-[[Film/TheFly1958 The Fly]] Bart and Witch-Marge (both from THOH VIII) where the Alien Maggie incinerates the OddOneOut, Lisa "as an axe victim", as soon as the latter [[FridgeLogic questions what aliens have to do with Halloween]][[/note]].
* ScrewedByTheNetwork: Creator/{{Fox}} has been generally unable to schedule these episodes within the week before Halloween since buying the exclusive rights to the [[UsefulNotes/{{Baseball}} World Series]] in 2001.
** This was even lampshaded in one special when the episode aired passed the Halloween holiday with Kang and Kodos stating it was near Christmas time.
* UglyCute: The blue Gremlin at first... until the [[NightmareFuel ending.]]
* WereStillRelevantDammit: The post-SeasonalRot episodes ''stopped'' being scary and are instead just parodies of 'relatively new' movies and TV shows with BlackComedy (See WSRD on the main show's YMMV page).