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* {{Anvilicious}}: In "My Fair Mandy", Grim questions why anyone would participate in beauty pageants (Mandy is only doing it to show up Mindy). Cue several moms encouraging their daughters to win for the sake of their love.
* BadassDecay:
** When Grim first appeared, he was an actually competent and talented character, who people actually were intimidated of (apart from Billy who's too stupid and Mandy who fears no one). He still has some badass episodes, but most of the episodes after episode 3 shows him constantly being made a fool out of.
** ''Underfist'' reimagines Hoss Delgado as washed up and still hung up on his breakup with Eris, now sporting a beer gut and living with his mom. He gets his ass handed to him countless times throughout the movie.
* BaseBreaker: Fred Fredburger became this after being extremely overused in CN's promos along with the excessive overuse of his [[TrademarkFavoriteFood nachos]] and [[ToiletHumor poopoo jokes]].
** As was Mandy, in later seasons.
** Billy, between fans who find him hilarious and fans who find him annoying and one-note.
* BizarroEpisode: While the show is essentially a bizzaro ''series'', a few stand out from the pack.
** "My Fair Mandy" which [[spoiler: ends with Mandy's smile destroying reality and the main trio become WesternAnimation/ThePowerpuffGirls with Irwin as Mojo Jojo.]]
** "Complete and Utter Chaos" starts with the title card reading [[UpToEleven "Billy Gets Dumber"]] before Eris tears it down and puts in the real title card while whistling the title card theme tune. It escalates from there.
* BrokenBase: Over whether the show becoming increasingly DenserAndWackier was a good or bad thing.
* CrackPairing: Dean Toadblatt and a giant squid, canonically.
* CreatorsPet: Fred Fredburger. Being a huge BaseBreaker as well as an EnsembleDarkhorse, some see him as one. Along with being heavily advertised, he was shoehorned into and ''Billy and Mandy's Big Boogey Adventure''. One particular scene is when he swallows a cannonball and is injured as a result, Mandy ([[EnfanteTerrible the resident sociopath]], mind you) then turns to the Mandroid, saying Fred did not deserve that. Of course she said that only to check that her robot clone was as sociopathic as she was and was satisfied with the answer ''acceptable losses''.
* CrossesTheLineTwice: [[ChristmasEpisode "Billy and Mandy Save Christmas".]] Features such things as a mall being burned to the ground as the MallSanta is mercilessly beaten (with The Grim Reaper implying that this happens all the time and Billy blaming it on the sad state of the economy), [[BadSanta evil vampire Santa]], Santa's evil vampire wife, and [[CrowningMomentOfFunny the local bully being eaten by a pack of flying vampire elves.]] Quite subversive compared to the average Christmas episodes, and even fellow childrens' cartoons that try to subvert the usual sweetness of a Christmas special don't take it that far.
** A lot of the humor can dip into this, it being BlackComedy.
* CrossoverShipping: There's Mandy and Dib from ''WesternAnimation/InvaderZim''. It's actually pretty popular.
** One that arose not too long ago was teenage!Irwin and Marceline from ''WesternAnimation/AdventureTime''. It hasn't officially caught on, per se, put the creator has gotten some positive feedback for her [[PortmanteauCoupleName Marcewin]] art.
** Irwin's also been paired with [[WesternAnimation/PowerpuffGirls Buttercup]] and [[WesternAnimation/FairlyOddParents Tootie]]. By a few people. And this isn't the best place to be discussing our opinions on the "art" itself...
* DarknessInducedAudienceApathy: With how grim and crapsack the world is and how unlikable Billy and Mandy can be to some, this can happen.
* EarWorm: [[VillainSong BRAINS, BRAINS, I WON'T LIE. I'LL EAT THEIR BRAINS UNTIL THEY'RE ZOMBIFIED!]]
** The first end credits theme. "''Grim and Eeeeeeevil. Grim and Eeeeeeeevil.''"
** The title card theme is really damn catchy too.
** The end song from ''[[https://www.youtube.com/watch?v=x7kl47pE89k Underfist]]''.
* EnsembleDarkhorse:
** [[TheDitz Fred Fredburger]], [[VerbalTic yes!]] Though he became a BaseBreaker due to overexposure like [[WesternAnimation/FostersHomeForImaginaryFriends Cheese]].
** Jack O'Lantern has also gained himself a sizeable fanbase, [[OneSceneWonder despite only having appeared in a Halloween Special.]] [[PopularityPower This is possibly the reason he was included in the video game.]]
** Dracula.
** Skarr, the only mainstay from "Evil Con Carne".
** Admiral Wolverine Lightningbolt.
** [[GreekChorus Sir]] [[MetaGuy Raven]].
** [[{{Music/Voltaire}} The evil brain-eating meteor]].
** [[EvilIsSexy Eris]], the goddess of chaos.
** Hoss Delgado. He was popular enough that he ''nearly'' starred in the spinoff-series-turned-TV-Movie, ''Underfist''.
* EvilIsSexy: Eris. Never mind the gap in her teeth.
* FamilyUnfriendlyAesop[=/=]SpoofAesop: Billy learns from his inner frat boy that, just because someone is different from you, you shouldn't be afraid of them. You should be '''angry''' at them!
* FountainOfMemes: Probably one of the most quotable Cartoon Network shows ever, especially in the earlier seasons.
* GeniusBonus: The episode where Billy meets mushroom-growing dwarfs has a scene where he escapes from Yogi and Boo Boo by hiding in a cave. Brown bears really are afraid of caves. Ironic as Yogi and Boo Boo live in a cave in [[YogiBear their source material]].
** The show is filled to the brim with horror movie references, most of which are fairly obscure even to adult fans.
** Mandy quotes Creator/AleisterCrowley in one of her typical (very) cold openings: "To do what thou wilt shall be the whole of the law".
** Dracula may be based on Redd Foxx and the title character of ''Blacula'', but his appearance is actually pretty accurate when compared to the novel Dracula's originally from. The fact that he's not harmed by sunlight (save for his first appearance on the show) is also novel-accurate. This may or may not be AccidentallyAccurate, though.
* GrowingTheBeard: Generally agreed to be around the time this show split off from ''Grim & Evil''.
* HilariousInHindsight: In one episode, Grim is seen watching a Franchise/MyLittlePony parody called "My Troubled Pony" and enjoying it very much, in spite of the fact that he's a male adult and he's clearly not within the show's demographic. [[WesternAnimation/MyLittlePonyFriendshipIsMagic Fast forward to 2010...]]
** Nergal is a [[NoodlePeople tall and thin]] HumanoidAbomination with CombatTentacles and wearing a [[BadassInANiceSuit suit]]. Now [[Franchise/TheSlenderManMythos who does that sound like]]?
** In the beginning of ''Big Boogey Adventure'', Billy doodles "cops fighting dinosaurs" instead of writing out plans, and then remarks that "they should be working together" when Irwin calls him out. [[Webcomic/AxeCop It wouldn't be the last time that concept came up.]]
** An in-series example: in the beginning of ''Billy & Mandy's Jacked-Up Halloween'', Irwin's first Halloween costume is Sleeping Beauty, as a lame attempt to get Mandy to kiss him. Fast forward to ''Big Boogey Adventure'', and it's '''Mandy''' who's now the sleeping beauty that needs to be awakened with a kiss. And guess who kisses her?
** ''WeaternAnimation/MonsterHigh'' came out with a line of dolls called "Freaky Fusions", complete with an animated movie based on them. Obviously, the premise is based on [[HybridMonster Hybrid Monsters]]. It becomes funny when you realize that Maxwell Atoms already did this with the aforementioned Irwin. (Good thing they didn't do a mummy/vampire, otherwise he'd probably sue...)
** In the video game, Dracula and Irwin's victory quotes when beating each other become this (or maybe HarsherInHindsight, depending) when you realize Dracula is Irwin's grandfather.
** In one episode, Billy wears Junior as a magic pair of pants to help pass a fitness test. (ItMakesSenseInContext.) As pants, you can still tell it's Junior because he still has his eyes (and glasses). Hm, people wearing magic clothes with eyes... [[Anime/KillLaKill Why does that sound familiar?]] (Tumblr's certainly caught onto this one.)
** This wouldn't be the last time Creator/NikaFutterman voiced a character named [[VideoGame/KidIcarusUprising Pandora]].
* LauncherOfAThousandShips: Mandy, if you can believe it. She's been shipped with Billy, Grim, Irwin, Nergal Jr., [[FoeYay Mindy]]... Hell, [[CrackPairing even]] ''[[WesternAnimation/InvaderZim Dib]]''!
* MagnificentBitch: Whenever Mandy brings her A-game. One particular is when turned herself into a slug and tricking TheResistance into believing her [[WeaksauceWeakness weakness]] are frogs.
* MemeticBadass: Hoss Delgado.
* MemeticMutation: See OverlyLongGag on the main page.
** [[{{Music/Voltaire}} Well hello little boy! Don't be shy! Step right up, I'm a reasonable guy! Don't be frightened by the look in my eye, I'm just your average evil meteor from outta the sky!]]
** Judge? Where are the nachos?
*** Yes!
*** I can spell my name real good! F-R-E-D! F-R-E-D! B-U-R... G! E-R! [[TheDitz Fred Fredburger]], yes!
** YOU DON'T TELL DRACULA WHAT TO DO! DRACULA WAS BORN KNOWIN' WHAT TO DO!
*** Vampires don't suck! They scrape! And lick! Scrape! And lick!
** Pretty much EVERYTHING that [[FountainOfMemes Sir Raven]] says...
*** "Do not cry for him. DO NOT CRY!"
*** "YOU FOOLS! YOU'VE MESSED WITH THE NATURAL ORDERRRRRRRRRR!"
*** "IMPORTANT! COMMERCIAL! MESSAAAAAAAGE!"
*** "'''THEEEE!''' '''''EEEEEEEEEENNNNNNDDDDD!'''''
** Grim was the original brony.
** Grim's Peanut Song from Episode 2: "Look at me, I'm a kitty cat! I wear a bowl of peanuts for a hat. If I eat them all, I will get fat! Blah blah blah I'm a kitty cat!"
** LIKE AN ANGRY WOMAN.
** Lord Byron is Billy's [[Manga/JoJosBizarreAdventure Stand]]!
** DESTROY US ALL! DESTROY US ALL! [[https://www.youtube.com/watch?v=N9KGfgg-d8s DESTROY US ALL!]]
** That "WOG WOG WOG" creature thing that Grim is briefly shown summoning in "Skarred for Life".
* MisaimedFandom: Pretty much anyone who thinks Mandy is cute, since her [[TokenEvilTeammate evilness]] is supposed to make her the opposite.
** Mandy also seems like a feminist. As such, other real world feminists look up to her. Mandy really shouldn't be holding the feminist flag, though, because she's [[SociopathicHero sociopathic]], misanthropic, and [[{{Narcissist}} borderline narcissistic]]. It doesn't matter if she holds good feminist values or not because it's offset by her horrible actions and character.
** Some villains on the show getting the DracoInLeatherPants treatment is kind of to be expected, because they are a bit sympathetic. Then there's [[LightIsNotGood Bun]]-[[CuteIsEvil Bun]], who has no redeeming qualities and did plenty of pointlessly terrible things to the protagonists of ''Underfist'' for no reason. Yet somehow, for whatever reason, a small handful of fans like Bun-Bun and find him adorable.
* {{Moe}}: The show is surprisingly adorable for something so dark.
** Billy can be really cute so long as there's no [[GrossUpCloseUp Gross Up Close-Ups]].
** Nergal Jr. is considered this by most of his [[{{Fangirl}} Fangirls]]. It's probably the quiet voice and [[{{Adorkable}} dorkiness]].
** Irwin, when one thinks about it. He's also {{Adorkable}}, usually one of the nicer characters, is also a NonActionGuy most of the time, and is later revealed to be a CuteMonsterBoy. Vanessa Marshall's performance pretty much seals the deal.
** Mandy subverts and defies this, being absolutely ''nuts'' to the point where it hinders her from being cute. [[DoubleSubverted Unless, of course, you're into that kind of thing.]]
* MoralEventHorizon: Quite a few, though they're offset only by the show's NegativeContinuity (usually).
** Grim and Mandy have had a number of potential moments, usually involving leaving Billy to a CoolAndUnusualPunishment.
** Billy, though a good kid, has tried to kill his "adopted" son just because he's afraid of spiders.
** Irwin has allowed a Pyramid to be built in his honor, regardless of whether or not everybody remains brainwashed.
** Nergal forces a number of people, including the viewer, into transforming into his "[[WasOnceAMan Friends]]" in the second episode he appears in.
** Boogey crossed it in ''Wrath of the Spider Queen.'' During the contest for who would become the future Grim Reaper, Velma was close to winning, but Boogey decided to rig the voting. When Velma finds out, [[spoiler: she thinks Grim tried to cheat]], costing him his only friend.
** [[SadistTeacher Ms. Butterbean]] crosses it in ''Substitute Creature'' when she ignored Sperg bullying Junior because he bribed her with an apple. The drawer filled with apples makes clear that this has happened lots of times. To really [[KickTheDog twist the knife]], she tells Junior that it's okay for Sperg to do it because he was bigger. You don't feel bad when Junior glues her to the ceiling and takes her form.
** Mindy has had her fair share of candidates from attempting to incinerate Mandy for taking her place as cheerleader of the team to beating up Billy with knuckles for being a loser. And let's not even mention Underfist...
** Sperg outdid even his usual abusive self by resorting to cannibalism and eating Pud'n.
* MostAnnoyingSound: DESTROY US ALLLLLLL!!! DESTROY US ALLLLLL!!!
** To a lesser extent, any time Billy laughs.
* NauseaFuel: Several times in the show.
** Many of the injuries, such as when Pud'n [[EyeScream gets an eye full of cactus and pulls it off, revealing a hideous, skinless red eye]].
** Or Billy's nose popping.
** Or when the closing iris closes on Billy's head and a bunch of blood and snot sprays from his nose and his eye pops out.
** Or when Billy and Mandy force Grim to resurrect the school mascot cats. That, in itself, is pretty bad, but when Billy asks one of the cats to scratch his back...his skin and muscle get shredded by the splintered claws of the undead cat, and his spinal column pokes out.
** In the episode, "Zip Your Fly," Mandy accidentally swapped her head with that of a fly after messing with Grim's zipper. That's pretty standard for the show, but then after losing the zipper to the dump, she ends up eating ''the entire landfill'' before she can find it and get her body back.
* TheProblemWithLicensedGames: Averted. The video game based on the series is a surprisingly fun beat-em-up style fighter with plenty of characters from the show, all voiced by their actual voice actors, with Music/WeirdAlYankovic as the announcer!
* SeasonalRot: The final season is considered the weakest season, though Underfist is well-regarded.
** The second or third season after being split from ''WesternAnimation/EvilConCarne''; by then, its AdoredByTheNetwork status made it considerably less enjoyable. Though as BrokenBase above indicates, some see it as GrowingTheBeard.
* SelfFanservice: Mandy gets a lot of fanart that depicts her as incredibly attractive despite her having no nose and characters in-Universe reacting to her as if she's hideous (she was once mistaken for "an angry tree stump").
* SpotlightStealingSquad: Irwin in later episodes. Most obvious in Underfist.
* TearJerker: In "Son of Nergal", Junior attempts to fix his teddy bear, Mr. Bonkers, after Mandy rips its head off.
-->'''Junior''': It's *sniff* going to be okay. I'll put you back together and *sniff* you'll be my friend and I'll be your best friend...
** Billy saying goodbye to his pet chupacabra Daisy.
** The flashback in ''Wrath of the Spider Queen.''
** A few shots of Irwin crying in "Irwin Gets a Clue". And the end, sort of.
** The end of "The Greatest Love Story Ever Told Ever". Turns out Mandy was just messing with Irwin and Junior's emotions.
* ToyShip: Admit it- you've all considered this for Billy and Mandy at least ''once''.
** Or Irwin and Mandy.
** [[HoYay Or Billy and Irwin]].
** Or Junior and Mandy, to a lesser extent than the other two.
** Or Junior and Irwin. It's not as popular as some of the other pairings, but it's had a few hints dropped in the show.
* UnintentionallyUnsympathetic: How unintentional is up for debate, but Irwin, Pud'n, and Sperg in "Tricycle of Terror" fall into this trope. While it could be argued that Billy was indeed too old to be riding a tricycle, this doesn't excuse the fact that all three of them sadistically mock him for it, with Sperg taking it a step further by giving Billy a brutal wedgie and then throwing "Trikey" off a cliff while Billy can only watch and beg helplessly, with all three of them gloating about [[EvilFeelsGood how good it felt]] after doing so (Pud'n even calls it "awesome", the little shit). When the haunted tricycle violently retaliates, they all have the nerve to expect sympathy from both Billy and the audience, with Pud'n obnoxiously calling Trikey a "mean old tricycle", conveniently ignoring the fact that they are all [[AssholeVictim Asshole Victims]] who went out of their way to deserve their fate. It also doesn't help that Trikey, unlike {{Literature/Christine}}, doesn't attack people for simply being close to Billy and only attacked Grim out of self-defense.
** Mandy, most of the time. She has a few moments/episodes here and there where she's put in a position where she ''should'' be TheWoobie. She's the EnfantTerrible TokenEvilTeammate, though, and her actions towards others seem like a major case of DisproportionateRetribution, so it's almost impossible to feel something for her.
* WhatDoYouMeanItsForKids: Like nearly all of Creator/CartoonNetwork's in-house programming (specifically those from the "Cartoon-Cartoon" era of shows), this show is a kids' cartoon on the outside, and on the inside, is packed with a lot of things that most normal channels wouldn't allow to touch children's animated shows. In the case of this show, it's BlackComedy, some mild sex and toilet humor, and disturbing imagery that makes ''WesternAnimation/InvaderZim'' look like ''My Little Pony''.
* WhatTheHellCastingAgency?: Creator/GilbertGottfried as ''SantaClaus''.
* TheWoobie: Pud'n and Jeff. Also, Skarr. He is just trying to move into the neighborhood, trying to avoid his previous life as TheDragon[=/=]TheStarscream.
** Billy, at times.
** Nergal Jr. is a WoobieDestroyerOfWorlds. He just wants [[IJustWantToHaveFriends friends]] and [[IJustWantToBeLoved love]], but it almost never works out and he's the constant victim of bullying and bad luck. And seeing as he's an EldritchAbomination, things can get ugly when he's hit his RageBreakingPoint.
** Irwin's life is kinda sad, actually. He has a crush on the most evil girl in the world (who hates him), wants to be cool (but fails miserably), and some of the horrible things that happen to him happen for ''seemingly no reason''. Add in the fact that he's usually not as much of a jerk as the other characters, is {{Adorkable}} in his own right, and that his crush on Mandy is [[FridgeBrilliance probably Billy's fault (remember "Get Outta My Head!"?)]], and you've got a pretty solid candidate.
** JerkassWoobie: Grim has his moments too.
*** Mandy may act in an evil manner, but if you think about it, she has her reasons. She has to deal with Billy every day, Mindy is on her neck all the time, she's not allowed to smile or else the world will either end or get seriously messed up.
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