"Boo York, Boo York" (also titled Boo York Boo York: A Monsterrific Musical!) is the twelfth TV special produced for the Monster High cartoon series and is meant to be a musical. It was released on September 29, 2015. The TV special ties into the Boo York, Boo York - City Ghouls, Boo York, Boo York - City Schemes, Boo York, Boo York - Gala Ghoulfriends, Boo York, Boo York - Frightseers, Boo York, Boo York - Comet-Crossed Couple, and Boo York, Boo York - Out-of-Tombers lines.
After performing ("Love is Like a Storm Tonight"), Catty runs out of ideas for writing a new song, so she sings ("Search Inside") to say that she should "search inside" of herself for ideas on a love song. Meanwhile Ramses de Nile sees the crystal comet arriving and he and Nefera prepare to head to Boo York. He also informs Cleo and allows her to take a friend or two with her. However, she invites Deuce (as well as giving him a King Tut-like chin piece and gold glasses), Frankie, Clawdeen, Draculaura, Operetta and Catty.
The crew head to Boo York where they shop for new clothes and wear them out.("Fright Lights, Big City") Luna Mothews, a moth monster girl also arrives and meets them. Cleo takes Deuce with her and turns out Nefera has also invited Toralei. The ghouls also encounter Elle Eedee, a robot DJ who is playing her music on the streets. Cleo, Nefera and Deuce end up in the same taxi as Mouscedes King.
Meanwhile, Ghoulia finds out a comet is about to land on Earth. The De Niles meet Lux Ptolemy and her son Seth. She then is disgusted at Deuce's informality. Back at the catacombs, Abbey walks in to find Ghoulia attempting to stop the comet from arriving. Ramses and Nefera devise a plan to invade Boo York ("Empire"), while the latter herself plans to get rid of Deuce who she believes is in the way of their plans.
Next morning, the De Niles, Ptolemys and the other ghouls settle down at a banquet, only for Deuce to dress like going to the beach, embarrassing everyone. The guards then put him in a blazer which catches fire on a candle since it's too loose. The fire is extinguished but everyone is affected. Nefera later convinces Deuce he doesn't belong with Cleo. At the same time Ghoulia tracks down the comet only to find it will land in Boo York. Later that day, the ghouls run into Luna who now works for a pizza parlor.
Ghoulia uses satellites in attempt to repel the comet, which turns out an alien is inside it, but it persists. Elle then reacts to the comet, but neither herself nor the ghouls can tell what's going on. The ghouls are about to take the subway to catch up with Cleo, when they meet a rapper named Pharaoh, who takes an immediate liking to Catty. The duo then make an escape from the crowd of Catty's fans. Deuce approaches Cleo and painstakingly breaks up with her ("It Can't Be Over").
Back at Monster High, the catacomb door is left open, allowing Heath and Manny to witness the comet coming closer to Boo York. Meanwhile, Pharaoh takes Catty to the Monster of Liberty where she hears the sounds of Boo York as music, realizing she finally found the music she has been looking for.
The ghouls, including Catty later dress up for the crystal comet. Nefera convinces Cleo that Deuce isn't worth being with. Ghoulia, still trying to make the comet land safely now that she finds life inside it, is interrupted by Rotter, who joins Manny and Heath in witnessing the comet. Later that night, Catty parts ways with Pharaoh after being able to write a new song of her own.
The crystal comet party commences, with the ghouls, Ptolemys and De Niles attending. Elle is their DJ. The ghouls then realize something's not right when they see Deuce hasn't been with Cleo. Luna also works there as a waitress. With more students witnessing the comet landing back at the catacombs, Ghoulia continues using the satellites to stop it. However, the radiation is deflected and triggers both the crystal comet shard and Elle.
Cleo takes a look at the hieroglyphics and sees herself and Deuce in it, realizing they still belong together. Luna also changes out of her uniform right before Cleo and Seth are to have a promise ceremony as the two of them are destined to summon the comet together. Halfway, Seth takes off his mask and reveals he is indeed Pharaoh, then speaking up against Lux. He sings ("Boo York, Boo York") with Catty and they escape after that.
At the roof top, Nefera steals their voices (they can still speak, but can't sing properly) using the crystal comet shard. Toralei then sneaks off with it and takes Catty's singing voice to perform at Bloodway. The ghouls then confront her musical-style, ("Steal the Show"). Luna not only returns Catty her voice but earns herself fame at Bloodway. Mouscedes then summons taxis for them to return to the promise ceremony. Deuce, who believes he still belongs to Cleo despite their differences, joins them.
Back at the tower, Toralei calls Nefera to inform her she lost the comet shard. An enraged Nefera uses an amulet that drains all the power in Boo York. The gang then end up in a traffic jam so they have to scale the roofs of Boo York, but during it Elle malfunctioned and Frankie and Draculaura called Ghoulia and Abbey for help. They arrive on time and Deuce reunites with Cleo. Seth/Pharaoh voices his following his own path after Catty brings back his voice, this time Lux lets him.
At the post-credits scene, Astranova, who now attends Monster High, starts a music battle with her guitar against Operetta and her banjo during Rotter's class. After class, Astranova calls Ever After High's Raven and Apple, telling them that Monster High actually exists.
- The movie's title is a reference to the 1977 song "New York, New York" composed by Kander and Ebb and popularized by Liza Minnelli, later covered by Frank Sinatra.
- Boo Jersey is a pun on a real place in the United States, New Jersey.
- Creeperoni pizza is a pun on pepperoni pizza.
- Boocci is a pun on a company named Gucci mostly for men.
- Elle's name is a pun on LED.
- Astranova, Elle Eedee, Luna Mothews, Mouscedes King, Seth Ptolemy, and Amuncommon Ptolemy make their 3D cartoon debuts.
- When the ghouls are talking to Ghoulia and Abbey, when Elle is flawed/malfunctioning, she is using her Boo York, Boo York - Gala Ghoulfriends outfit, but is suddenly changed to Boo York, Boo York - City Ghouls outfit and then back to the previous outfit.
- Catty is missing her tail for almost the entire movie.
- One of Nefera's hangups is her shame over her birthmark on her left shoulder. She keeps it hidden at all times, hence why her Boo York, Boo York - City Schemes doll has a shoulderpad on the left. This outfit is treated as a gala look, while Nefera walks around in the dress without the armor portion for the rest of the movie. This would leave her birthmark exposed, something she'd never do, though it also shows Nefera's model lacks the birthmark. On a lesser scale, Nefera walks around without headwear for most of the movie, yet her hair is shaped as if something's lying atop it.
- It isan error for Operetta to even try to mimic Catty singing as showing that she wants Catty to sing, because according to the webisodes and doll diaries, her voice is supposed to literally be only safe to listen to on a recording, therefore, if her singing is only safe to listen on recording and not live, it should not even be possible.
- A soundtrack containing all the songs from the movie was released on September 25. The soundtrack contains 8 original songs from the movie as well as the recent theme song, We Are Monster High, and the old one as well. Most of them are composed by Catty Noir.
- Lagoona Blue was originally supposed to play a supportive role in this movie, where she accompanied the ghouls to Boo York and went on a separate adventure with Frankie. Plans for this sideplot included a midnight visit to a museum and the discovery of a giant girl living in the Boo York sewers.
- The post credit Ever After High scene was thrown in at the last second. The final scene was supposed to be them in the school pool, listening to the song "Boo York, Boo York".
- The DVD of the special contains the Spring Unsprung special from the spin-off series, Ever After High.