* ActorAllusion: Creator/ErinFitzgerald, who voices Elle Eedee, "voices" [[Characters/LeagueOfLegends Sona]], another blue haired popular musician/DJ.
* DevelopmentHell: A LiveActionAdaptation musical was planned for 2012. The musical part got carried to the 2015 CG movie ''Boo York, Boo York'', and the live-action part was a scrapped EverAfterHigh crossover.
* FakeBrit: Julie Maddalena as Robecca Steam, Stephanie Sheh as Jane Boolittle, and Jonquil Goode as Ari Hauntington.
* FakeNationality: Pretty much every foreign character. Technically averted with Stephanie Sheh as Jinafire Long, as she is American, but of Taiwanese descent.
* FanNickname: Sixties Chick and Scary Lou for Scarah, Lala for Draculaura, and [[Series/DinersDriveInsAndDives Guy Fieri]] for Heath.
* FollowTheLeader: With the line being a top seller, you bet there are imitations. MGA, before they took a break to rebrand Bratz, expanded the line with Bratzillaz, the witch "cousins" of the Bratz. They're best to copy MH in presentation - a quick check of the Bratzillaz Youtube channel had webisodes and a live-action music video. FandomRivalry was strong here.
** Novi Stars: MGA's line of dolls with an alien gimmick and Punny Names. They're also following the music video and webseries trend.
** Playhut came out with Mystixx, which copy the look of the Monster High dolls (with some possible recasting of the Mattel molds) and features some possibly traced character art.
** Midnight Magic, a line of multi-colored witch dolls found mostly at discount stores, and a slew of various bootlegs and copycats coming from China.
** WesternAnimation/MyLittlePonyEquestriaGirls is WesternAnimation/MyLittlePonyFriendshipIsMagic getting a Monster High-like makeover.
** Even comics can't resist, as Franchise/TheDCU now has its [[Franchise/DCSuperHeroGirls own line of various female characters going to high school]] (in all fairness however, DC was pushing for that to happen even well before Batman Beyond was created- but likely went ahead now thanks to other similar lines being successful). Granted, the merchandise is another Mattel property, not another company.
** Of course, Monster High itself wasn't exactly immune to this, as it could be considered similar to at least THREE earlier cartoons, for example ''Scooby-Doo and the Ghoul School''.
*** The Hanna-Barbera 1990s cartoon ''Gravedale High'' featured the usual monster stereotypes in high school, with a human teacher(voiced by and modeled after Rick Moranis) that may be a direct inspiration for Lou Zarr.
** The Save Frankie and fusion cosplay lines were invented for the Freaky Fusion toyline, without appearing in the film.
** Despite being part of the ''Welcome to Monster High'' toyline, "Dance the Fright Away" Abbey and Moanica do not appear in the film, with Abbey herself not appearing in any form.
** There is another, completely unrelated movie [[Creator/AllisonPregler Obscurus Lupa]] reviewed called ''Monster High'' (that predates the franchise by almost 20 years) which contains gory shots of people exploding and gratuitous amounts of RapeAsComedy. Pray that an unwitting parent hasn't confused the two.
** Shortly before the series debuted, a children's book titled ''Frankie Stein'' was published, about a young boy monster built much like the Frankenstein monster.
** Deliberately invoked in-universe with Dracula- Draculaura's adoptive father is NOT the well-known Dracula. Vlad the Impaler took the title for himself several centuries after this Dracula served the Roman Empire. The two did have a conflict over it.
** Clawdeen shares her name with a pink lion from the WesternAnimation/SheRaPrincessOfPower toy line- a result of Mattel recycling an old trademark.
** Deuce, starting with the "Why Do Ghouls Fall in Love?" special, is now voiced by newcomer Evan Smith. Smith also replaced Yuri Lowenthal as the voice of Gil. Cam Clarke filled in as Deuce's VA until Evan was cast. The vocal change also marked a [[SameCharacterButDifferent change in his personality]] that not everyone agrees with.
** Clawd was initially voiced by Yuri Lowenthal for "Fur Will Fly" for only one line; he's currently voiced by Ogie Banks.
** Heath was voiced by Yuri Lowenthal in Season 1, but Cam Clarke voices him in Season 2.
* TalkingToHimself: Since there are more characters than voice actors, this happens a lot.
** Audu Paden voices Manny, Slo-Mo, and Ghoulia.
** Salli Saffioti voices Cleo and Clawdeen.
** Erin Fitzgerald voices Abbey, Cupid, Rochelle, Scarah, Spectra, Clair, Fawn, Wydowna, and Elle.
** Evan Smith voices Deuce, Invisi Billy, Garrott, Gillington, Rocco, and Thad.
** Cam Clarke voices Heath, Hoodude, and Mr. Rotter.
** Cindy Robinson voices Gory, Holt, Jackson, Madame Ghostier, Operetta, and Lux Ptolemy.
** Laura Bailey voices Bloodgood, Lagoona, Honey, and Skelita.
** Stephanie Sheh voices Jinafire and Jane.
** America Young voices Toralei, Howleen, and the werecat twins.
** Kate Higgins voices Frankie, Iris, Lilith, and Casta.
** Jonquil Goode voices Clawdia, Gigi, Djinni, Twyla, and Ari.
** Haviland Stillwell voices Avea and Vandala.
** Paula Rhodes voices Iris and Sirena.
* PropRecycling: The dolls often reuse shoe and accessory molds to cut down on costs, though it's usually a different color. The most blatant case would be Gooliope's Shriek Wrecked purse, which is just a scaled-up recolor of Vandala's to fit Gooliope's giant theme. This has even been done with some faces. Ghoulia and Cupid share a face, Amanita uses the Create-A-Monster Vampire face, Catty and Toralei share a head mold as well.
* ShowAccuracyToyAccuracy: Most of the time, the dolls are pretty good representations of their depictions in their character art, the webisodes, and the movies, but usually their faces are much milder. Some more notable inconsistencies include:
** Gil's dolls have a layer of head scales to simulate shaved hair around his fin "hair", similar to Deuce and some scales on his chest. However, the cartoon version has a completely smooth head and chest. Gil's also lacking a doll of his signature outfit, due to his limb fins preventing him from wearing long sleeves and pants.
** The CGI art on Kiyomi's box gives her a pink hair accessory and silver chain earrings similar to her belt. The doll itself has a sea green hair accessory and simulated pierced ears, but no earrings.
** Animated Toralei's hairstyle is more like a pixie cut, but her dolls give her a neat bob style, and until the reboot, her dolls only had a feline nose shape, but not the black color.
** Spectra's dolls tend to look off, thanks to the stoic expression and totally straight hair as opposed to the constant cheerful smile and unkempt hair.
** Animated Elle's hairline is a squared-off widow's peak to keep with her angular robotic details. The actual doll's hairline is completely smooth.
** A detail that almost made it: Posea's animation model and artwork have gills on her face, but this feature never made it past the physical doll's prototype.
** The artwork for Gigi's "School's Out" doll gives her a low ponytail with hair swept across her face, and a small section of her midriff is visible. The doll's hairstyle is a high ponytail, and her outfit is one piece.
** Twyla's Freak Du Chic artwork lacks the fishnet sleeves that the doll's outfit has.
** Draculaura in Recap/WelcomeToMonsterHigh has a right forearm's worth of bangles, a punk multicolor-studded bracelet on her left arm, and tights under her dress. These are not present on her doll. Also from this movie, Moanica's boots have more detail in their painting and her belt is different.
** Ghouls' Getaway Spectra's art includes some pink tribal facial markings, but the doll has none.
* TheOtherDarrin: A few of the voice actors changed for the reboot.
** Prototype images indicated that Clawdeen (and presumably other werebeasts) was going to have her ears mounted on a headband rather than molded onto her head.
** Early images of Wydowna and Scarah show differences; Scarah was to have a Letterman jacket and Wydowna lacked her comic-book theme, instead wearing a fairly ordinary gingham dress.
** Posea Reef's prototype and artwork show that she was going to have gills on her face, but the final doll lacks these.
* ''Boo York, Boo York'' is the only line of dolls so far to include dolls of every standard body size (little sister-2, in fact-, standard, big sister, and male.) Since the stand design is new, it is also the only line with a different stand and all of the body types.