Over the years, not every idea brought up to expand Monster High made it to a product. There's about one to two years between concept and execution and much can happen in-between. Monster High itself, for instance, came close to being scrapped in 2009. An incident of significance that ties into the cancellation of approximately half the items on this page is the reboot in 2016, a result of the decreasing sales since 2013. Cancelled content, much like preliminary names, come to light through trademarks, toy listings, fiction, preparational content, and sometimes by creators talking about it.
- Euna — Euna, a kumiho, was to debut in the Monster High-Ever After High crossover movie "Feary Tale", but as the movie was cancelled in 2015, so did the character lose out on her debut.
- Jean Claw — The name "Jean Claw" was trademarked on February 23, 2012 and abandoned on April 15, 2013; at the same time as Ghouls Rule and a few months before anything related to City of Frights. This means it can be both a male name (French) and a female one (English).
- 1950s students — Before the story of Freaky Fusion reached its final form, there was a script in which the protagonists would travel through time to the 1950s. At least ten students from the 1950s were considered to meet the protagonists, five of which mono-types, the other five hybrids.
- The giant girl — The October 04, 2015 entry of Byron Leboe's Tumblr account notes that a giant girl was an early possiblity for the new characters to be introduced in Boo York, Boo York. She did not make the cut.
- Lux Ptolemy — "Lux Ptolemy" was trademarked at the same time, May 09, 2014, as "Seth Ptolemy", and abandoned on July 06, 2015. The forename was reused for Lux de Nile (Generation 2) on August 10, 2016, thus suggesting a male mummy identity.
- Lycana Wilde — "Lycana Wilde" was trademarked on December 09, 2015, a few days before Silvi Timberwolf on the 21st, and abandoned on July 03, 2017. The name is a pun on "lycanthropy" and points at a female werewolf.
- Russian Leshey — For the third wave of Monster Exchange, the inclusion of a leshey from Russia was planned. It was to have product number CHX70.
- South African Lightning Bird — For the third wave of Monster Exchange, the inclusion of a lightning bird from South Africa was planned. It was to have product number CHX72.
- Unicorn — A notable sight on the Zombie Shake packaging was the centered silhouette of a female unicorn amongst reused silhouettes from Dawn of the Dance. The silhouette was also used during the A Night in Scare-adise: Prom 2014 event.
- Griffin-based Fright-Mare — A griffin-based fright-mare was to be included in the fifth wave of Fright-Mares. It was to have product number DJF24.
- Dragons-based Fright-Mare — A dragon-based fright-mare was to be included in the fifth wave of Fright-Mares. It was to have product number DJF25.
- Seth Ptolemy — "Seth Ptolemy" was trademarked on May 07, 2014. As detailed on MHMonday, he was to have been a doll and would've been packed with Catty Noir as a second Boo York, Boo York - Comet-Crossed Couple 2-pack. The plan fell through early on and the aforementioned Catty doll became part of the Boo York, Boo York - Out-of-Tombers 3-pack.
- Tiki — Ghouls' Getaway, originally to be released as Return to Skull Shores, was conceived with the intent for each doll to come with a Tiki figurine.
- Gory Fangtell — Gory was an also-ran of the doll election of 2014. However, she was trademarked prior on August 08, 2014 and received focus time in "Boo York, Boo York" and "Decomposition Class". As per the fate of the 2011 also-rans, she would have likely received a doll after the winner, probably in the first half of 2016.
- Quill Talyntino — Quill was an also-ran of the doll election of 2014. However, she was trademarked prior on August 15, 2014, at the same time as Finnegan Wake, and received focus time in "Decomposition Class". As per the fate of the 2011 also-rans, she would have likely received a doll after the winner, probably Mid 2016.
- Spelldon Cauldronello — Spelldon is mentioned in Kieran Valentine's SDCCI diary of 2015, notably being referred to by a full name. Based on precedent, a doll release would've fallen between Mid 2016 and Mid 2017.
- Dedyet de Nile — "Dedyet de Nile" was trademarked on August 10, 2016, along with the names of several family members of the main cast, and abandoned on June 26, 2017. Based on the others, a doll was a possibility for Mid 2017.
- The Sea-Mares — "Sea-Mares" was trademarked on November 26, 2014 and abandoned on February 01, 2016. Because the critters appear in "Great Scarrier Reef", they have to have been meant for the accompanying doll series and would therefore have seen release in the final months of 2015.
- Classroom Draculaura — A Classroom doll was planned for Draculaura to be released in 2011. It was to have product number W2559.
- Country Wydowna Spider — Between her prototype display during the 2011 doll election and her eventual release in 2013, Wydowna underwent a style change from country to rock-and-roll geek. The original dress did form the inspiration for her I Heart Fashion set in 2014.
- Luxury party fashions for Lagoona Blue and Ghoulia Yelps — One piece of artwork released for the Sweet 1600 shows Lagoona and Ghoulia in fancy dresses among a group wearing Sweet 1600 and Dawn of the Dance clothes. The fact they themselves aren't in Dawn of the Dance fashion points at cancelled 2011-2012 dolls.
- Party fashions for Clawdeen Wolf, Cleo de Nile, and Frankie Stein — Three fiction-only party dresses for the aforementioned characters show up in "Night of a Thousand Dots", "Boo Year's Eve", and "Gloom and Bloom, Part 1 and Part 2. Given the styles and timing, they may have been meant for Dot Dead Gorgeous.
- Skultimate Roller Maze Draculaura and Cleo de Nile — "Friday Night Frights" features Draculaura and Cleo in Skultimate Roller Maze uniforms; the former even prominently. Like the rest of the line, they were probably meant for 2012.
- Picture Day Clawdeen Wolf — Most of the Picture Day fashion, released in 2012-2013, show up in "Franken-Styled", but Clawdeen's outfit has not been made into a doll.
- 13 Wishes - Haunt the Casbah Howleen Wolf, Cleo de Nile, and Ghoulia Yelps — "13 Wishes" features the three aforementioned lantern-ified looks, though none of them received a doll in the 13 Wishes - Haunt the Casbah line.
- Party fashions for Lorna McNessie, Gillington "Gil" Webber and Holt Hyde — "Gloom and Bloom, Part 1" and "Gloom and Bloom, Part 2" show the three in unique outfits. Lorna's matches the Gloom Beach look, while Holt's reminds of Dot Dead Gorgeous. Gil's fashion doesn't point any particular way.
- Fraidie Hawkins Headless Headmistress Bloodgood, Invisi Billy, Scarah Screams, Heath Burns, and Abbey Bominable — As detailed on MHMonday, the original plan for a Late 2015 5-pack was a Fraidie Hawkins one, following on the dance's importance in I Only Have Eye for You. It was to include the aforementioned characters in two couples and with Bloodgood in the role of chaperone. The idea was scrapped and replaced with Maul Monsteristas, to which only Invisi Billy made the jump.
- Great Scarrier Reef Gillington "Gil" Webber — Gil is one of the students to be transformed into a legless sea creature, but he is the only not to have received a doll.
- Gory Gazette w/ Spectra Vondergeist — As shown in leaked survey pictures in 2014, the Haunted line was to contain a playset of the Gory Gazette in accordance with its appearance in "Haunted". It was to have product number CDG14. The Spectra supposed to be included was eventually released on its own under product number DGB30.
- Salty Spectre — On April 28, 2014, the name "Salty Spectre" was trademarked. It is the ship of Vandala Doubloons in "Haunted" and likely was meant as another playset for Haunted. The trademark was abandoned on June 29, 2015.
- Garden Ghouls - Teeny Critters — Evidenced by an early stockphoto and store listings, such as Amazon's, a series of high-detail charms to hang in Treesa Thornwillow's branches was planned to be part of the Garden Ghouls lineup for release some time in 2017.
- Various fashions — The web game Teen Scream Freaky-Fab Photo Shoot contains a huge amount of fashions, some of which produced for the dolls, some of which unique to the game. A few of the game-only designs are of such detail that they likely were once considered for a doll.
- Eco-friendly fashions for Frankie Stein, Clawdeen Wolf, Cleo de Nile, Draculaura, Lagoona Blue, and Abbey Bominable — The environmentally conscious outfits show up in "Unearthed Day" and "Franken-Styled". These may have been intended as fashion packs.
- Party dress for Robecca Steam — Both Robecca and Venus appear in "Boo Year's Eve" in unspecified dresses, yet without different hair styles. Venus's outfit was eventually included in her I Heart Fashion release in 2014, possibly scavenged from unreleased fashion packs when those went out of style during 2012, but Robecca's remains without doll counterpart.
- Various fashions for Venus McFlytrap, Deuce Gorgon, Heath Burns, Draculaura, Clawdeen Wolf, Lagoona Blue, Frankie Stein, Cleo de Nile, and Abbey Bominable — "Scaris: City of Frights" features a lot of unique outfits, but only those belonging to the 'To Howl For' series saw release.
- Operetta — A vinyl figure of Operetta was on display at American International Toy Fair 2016, but it never saw release. It was to have product number DJC38.
- Jinafire — A vinyl figure of Jinafire Long was on display at American International Toy Fair 2016, but it never saw release. It was to have product number DJC39.
- Ghouls Skullection Wave 5 — The fifth edition of the mini figure collection would've contained Moanica D'Kay, Draculaura, Clawd Wolf, Catrine DeMew, Venus McFlytrap, and Frankie Stein and likely been released in the months May-to-July of 2017. It wasn't. Their product numbers in order are DYC68, FFN56, FFD28, FFD27, FFD26, and FFD25.
- "Feary Tale" — Commonly known as '"The Lost Movie", "Feary Tale" was a crossover movie with Ever After High and supposed to succeed "Great Scarrier Reef" in Late 2016. It was cancelled in 2015 due to Monster High getting rebooted and Ever After High being cancelled.
- "Shriekwrecked" — Shriekwrecked, Shriekwrecked - Shriek Mates, and Shriekwrecked - Nautical Ghouls is designed to go with a story, presumably a webisode series like Freak Du Chic before it, but none was ever produced. Instead, a three-parter stop-motion series was made, which has limited connection to the story setup as described on the back-of-the-box blurb.
- "Garden Ghouls" — Garden Ghouls, Garden Ghouls - Wings, and Garden Ghouls - Winged Critters is designed to go with a story, whether told in the form of a TV special or webisode series, but none was ever produced. Instead, a multi-parter stop-motion series was made, which has limited connection to the story setup as described on the back-of-the-box blurb.
- Fynn — Operetta's best friend from back home to whom she dedicates her diaries has been mentioned several times, but little about their character has ever been revealed.
- Spectra Vondergeist — Spectra's first diary points at a painful family history Spectra would rather forget. It's never been elaborated what that family history is.
- Smokey — Deuce's dragon pet, who got petrified by his gaze years before, never was written as having snapped out of it.
- C.A. Cupid — Cupid's origin story was cut short by her transfer to Ever After High. What is known is that she was left on Eros's doorsteps as a baby for unknown reasons. Even her monster type, hinted to be bone elemental, is unconfirmed.
- Jane Boolittle — Jane's origin story also is left open. All that is known is that she was found alone in the jungle with her staff and her companion, Needles, and that both are linked to her roots somehow.
- Gooliope Jellington — And lastly, Gooliope's origin story is unfinished. She's marketed as the daughter of "unknown", with said unknown's initials being R.S. and it being hinted that unknown is a mad scientist. Like Cupid, she was left to be found by others, in her case a circus.
- Monster High — Although the history of Monster High has been elaborated on many times, the exact origin hinted at during Freaky Fab 13 has not.