"Freaky Fusion" is the tenth big Monster High TV special and twelfth overall. It premiered as a digital release on September 16, 2014, and was followed by a home video release on the 30th of September as well as a television air date on the 6th of October. It is part of Volume 4, of which it is the first TV special. The tie-in lines of "Freaky Fusion" are five in total: Freaky Fusion, Freaky Fusion - Hybrids, Freaky Fusion - Freaky Fusions, Freaky Fusion - Fusion-Inspired Ghouls, and Freaky Fusion - Save Frankie!.
Frankie being is being chased by Creature 4.0. Neighthan comes to her rescue by throwing a casketball ball into the air, but he sadly crashes into the Bite-Centennial board. Frankie helps him up, and he asks when they get back to the others if they can skip telling them that part. Creature 4.0 squishes the ball with Frankie's face on it, and Frankie runs with Neighthan. Sirena Von Boo distracts the creature with her iCoffin and takes a picture of him on her phone. Then Avea and Bonita Femur come over to help them, and, having wings, lift Neighthan off the ground and Frankie jumps onto him. The scene does something that's like taking a picture and Frankie says she knows what we're thinking and goes on about Neighthan. She tells us that maybe it's the scary creature, and either way, she's sparked our attention. She begins to talk about how this is about family, but realizes they need to start from the beginning and then remembers that it needs to start at the opening titles. So she presses a button and it goes.
After the opening titles, it shows the Bite-Centennial theme at Monster High, which is a really big deal. Mr. Where comes over in invisible form, Clawdeen smelling his nasty stench, which he clears his throat with a cough to let her know he heard her saying that his cologne smells "cheap". Clawdeen pretend-corrects herself, and talks about how he's their favorite invisible teacher and that he loves giving them A's. Cleo calls it "very smooth", and Mr. Where hands out the papers for lines for the reenactment play asking if they're ready. Frankie tells Mr. Where that they're bursting at the seams, and Mr. Where talks about how proud he is of the play. When he tells them not to be late and disappears off, Clawdeen turns around with all the girls, and tells them that the cologne smells worse than a zombie's gym bag. She tells Ghoulia no offense, and Clawdeen, Cleo, Frankie, Lagoona, Ghoulia, and Draculaura go off without her to their lockers. Clawdeen notices the new students and asks if there's something wrong with them. Lagoona tells her and the rest they're hybrid monsters. Cleo asks if they should have to make up their minds, to which Clawdeen remarks to that Cleo can't even make up her mind when she picks an outfit for school. The girls walk by them and Cleo comments that the hybrid students don't look very friendly, which Clawdeen comes back with to her that she doesn't look very friendly. Frankie looks at a cute zombie-unicorn boy, and trips and falls down. The boy comes to Frankie's rescue and Frankie introduces herself. Frankie tells him this is the part where he tells her his name. The only boy of the hybrid students gets nervous, and can't say his name, but a moth-skeleton girl tells Frankie his name, which is Neighthan, and a purple-skinned harpy-centaur girl tells him to come on. Frankie tells Neighthan that she thinks he and his hybrid friends are really going to like it at Monster High, which he says "Yeah, sure" to and the skeleton-moth girl tells him to come on again. Cleo then comments that she told them they didn't look very friendly, and Neighthan clumsily trips on the banner for the Bite-Centennial celebration. When he walks off her friends, Frankie sighs in a romantically swooned kind of way.
After that, Cleo is finishing giving her presentation of her genealogy project for a class assignment. She brings the point to who she claims in the most important in the De Nile family tree - her. Her servants carve her picture into the stone. She says her family has more pharaohs and queens than anyone else's, so she says she should win the project, though Mr. Rotter tells her it isn't a competition. It is Robecca's turn, and she gives her assignment on Hexiciah Steam. Robecca tells the class about her amazing father, Hexiciah and tells the class that he was a teacher at Monster High. Rotter goes on about being the professor's favorite student. Robecca explains how Professor Steam worked in the Catacombs, invented something every single day, and that one day, he invented her. Mr. Rotter reminds everyone about being his favorite student again, while whirling a pencil and dropping it. Robecca explains how her father went missing sometime after, so she's kept a time box thing ever since. She says that every time she looks at it, it reminds her how grateful she is that Hexiciah discovered the secret to creating life, to creating her. Rotter tells her it was very good, and brings out the next student to give her presentation - Frankie. She tells of how her grandfather was Victor Frankenstein and that he invented her father (unmentioned, but is the great famous Frankenstein's monster) and, unmentioned, also created Frankie's mother, the monster's bride. When Frankie says that's all she knows, Mr. Rotter asks "That's it?", but Frankie can only show the blueprints for making her and an empty photo album scrapbook. Rotter calls her completely unprepared and tells her to rewrite the assignment, leaving Frankie in tears. Next is Abbey, whose report is a tad long.
In the Creepateria, the ghouls are having lunch and Clawdeen is writing in her fashion-design book. Clawdeen asks to pass the dead-sea salt, which Robecca and Draculaura politely can't make up their minds which should get it for her. She, Clawdeen, gets it for herself angrily. Lagoona tells Frankie not to be sad about the whole scare-itage project thing with a bad grade, which Frankie tells her it's not that, but not knowing anything about her heritage. Jinafire asks Frankie if she can ask her parents, but Frankie explains about her father. Lagoona sips her soup, which is too cold and Jinafire heats it up for her. Lagoona unsure says it's much better, and Neighthan and his female friends come near their table. Frankie offers for them to sit with her and her friends, but the blue-haired harpy-centaur girl says it's unnecessary when Neighthan was going to accept. Robecca and her friends talk about looking for Hexiciah's journal in the Catacombs, and when they leave, Frankie is still smiling at Neighthan. When gone, Neighthan tells the blue-haired harpy-centaur ghoul that that those ghouls were nice and they could've sat with them, which the centaur-harpy girl tells him that he shouldn't be naïve, and that Monster High is just like all other schools, and that they'll be moving onto the next school within a few days. Neighthan says that's not true, but the moth girl who is also a skeleton agrees with her and says "Yeah, flaw. Not flaws. They don't know what it's like to have two. Right, Sirena?" The third girl, the mermaid-ghost girl whose name is Sirena, says she agrees with all of them, while building a model of Monster High out of food.
Meanwhile, outside of school, the girls are walking to something to help them get to the catacombs. They find it, and on that gravestone, Robecca pulls the gravestone's skeleton skull top, and it triggers the Catacombs elevator. When there, Toralei and Cleo are arguing, and soon, they are in the catacombs. After a long journey down the Catacombs, the girls find a part where it's so dark, Jinafire lights it up. Lagoona then swims down to drain the water out. They find themselves near a door which when Robecca opens it is a bottomless pit. Then Robecca says she doesn't understand, and when she opens it again, a wild animal dragon (not person-monster like Jinafire) bursts out fire and the ghouls quickly shut it. Ghoulia, being a supersmart girl like she is, puts down the time box and it activates something. They discover that the secret is "it's about time" and Robecca comments how that's so like her dad. The girls go inside and Robecca tells them not to touch anything, which makes the whole crowd look at Toralei. She tells them she's got it that she won't touch anything, and they ghouls look around. Cleo finds out that her headband is crooked in the reflection of something, which Toralei bothers her with. Robecca finds something about Victor, and Frankie is glad that she did, but it turns out that her grandfather went crazy. Toralei sneakily pulls something and a bunch of stuff happens. A blue light is embellished and it grabs all the girls into it. The girls reappear in another version of the room in the Catacombs. The ghouls go upstairs and realize Monster High is under construction. They find out that they're in 1814 and Frankie gets happy to meet her grandfather. They soon need to find Toralei before she causes any more destruction. Draculaura gets upset due to iCoffin reception being gone in this time period. She cries, and the girls go inside. They get a lot of stares because of their up-to-date fashion styles, and one monster tries to touch Cleo, which Cleo tells her it's a Ghostier original and that it's magnificent and tells her to move along. After, the ghouls are still looking for Toralei and she's somewhere stealing monsters' fashion wears. Frankie and Ghoulia are looking for Toralei, and Frankie notices a steamy doorway making its entrance up, and there appears, a robotic cyborg (half human, half robot), and Frankie recognizes him as Hexiciah Steam, Robecca's dad.
Frankie and Ghoulia sit down in the classroom, and they watch eagerly. It turns out, Mr. Rotter, as a student was lying about being his favorite and was actually Professor Steam's least favorite student. Meanwhile, a boy named Sparky comes up to the room for his scare-itage project. He says he doesn't have a scare-itage for being an orphan. He shows the class his project of his "family." Everyone laughs, because his family is unstable and has poor quality. Hexiciah tells him he is missing something, and he doesn't understand. Later on, Frankie meets up with Sparky and tells him how her grandfather found the secret to creating life. Frankie realizes she's said too much, and leaves, with Lagoona and Jinafire having already found Toralei. They leave to the catacombs, but not without being spied on first. The girls are ready to go back home to their time period, but it turns out Sparky followed them.
When the ghouls return to their time period, they realise they have become hybrids. While Frankie and Ghoulia are normal, Robecca and Draculaura, Cleo and Toralei, Lagoona and Jinafire, and Clawdeen and Venus have been fused together.
Confused and concerned about this, Frankie has Ghoulia stay behind in Hexiciah's office to repair the Time Portal while she takes her fused friends to deal with the dress rehearsal for Mr. Where's performance. When Mr. Where discovers what happened, Frankie and her friends concoct the ruse that it was a project for Mad Science class, which Mr. Where accepts before asking them to take their positions for the dress rehearsal. As it begins, Neighthan and his friends are walking past the auditorium when they hear Frankie narrating, and on Neighthan's encouragement, they go inside to watch the performance. When Cleo and Toralei take the stage, Cleo's rendition of Headless Headmistress Bloodgood impresses the Headmistress as she was walking past at the time with Nightmare. However, things begin to spiral out of control as Frankie's fused friends begin to lose control of their bodies, as Cleo and Toralei argue with each other, Robecca and Draculaura can't control their hover boots, Venus and Clawdeen have Clawdeen howl alongside Venus growing large, carnivorus plants, and Lagoona and Jinafire can't control Jinafire's fire powers. The whole time this is happening, Neighthan and his friends can barely watch the disaster unfold, with the skeleton-moth girl admitting that "these ghouls need some serious help. They're making me a nervous wreck!" By the time Frankie ends the dress rehearsal, Mr. Where has a few comments regarding what happened.
Outside, Frankie sits on the steps in sadness as she watches her friends. At that point, the blue-haired centaur-harpy girl encourages Neighthan to talk to her. Once he's able to, Neighthan offers Frankie the support of him and his hybrid friends to help her fused friends get better control of their bodies and abilities, though not without Frankie becoming so concerned about her friends that her neck bolts discharge some energy that lightly shocks Neighthan, before he points out his fellow hybrids watching from behind some bushes.
Meanwhile, as Ghoulia takes a break from the repairs to the Time Portal to get something to drink, after she leaves, Sparky arrives in the lab, and quickly finds himself inspired to build his next creation using the modern technology he gathers from the lab, including the Time Portal lens.
In the catacombs, at the student lounge, Sirena, the blue-haired centaur-harpy girl, and the skeleton-moth girl are playing Go Squish when they see Neighthan arrive with Frankie and "the new fusions". After the centaur-harpy girl mentions the dress rehearsal the girls put on, Neighthan properly introduces Frankie and her friends to Avea Trotter, the blue-haired centaur-harpy girl, Bonita Femur, the skeleton-moth girl, and Sirena Von Boo, the mermaid-ghost hybrid, who quickly turns her attention to a spider that dangles down in front of her before she goes after it. When Clawdeen asks how they can help, Neighthan explains that since they are sort of hybrids like himself and his friends, they all have their freaky flaws to deal with, like Bonita being easily startled, Sirena getting easily distracted, and Avea tending to interrupt a lot. Neighthan and his friends know what Frankie's friends are going through and want to help. Cleo is skeptical of the support, but Avea apologizes for their earlier behavior, while Bonita explains that they've been to so many schools before Monster High that they don't trust anyone. Frankie assures them Monster High is different and will accept them, but Avea is still skeptical, saying that they'll see for themselves if Monster High is willing to accept them. Jinafire then asks about Neighthan and his flaws, but while Neighthan explains that he gets some healing powers from his unicorn side of his family, his zombie side makes him a little clumsy, as demonstrated when he crashes into a vending machine after struggling to get a bucket off his foot, earning a bemused giggle from Frankie.
Meanwhile, Ghoulia returns from her refreshment break to discover the Time Portal lens missing. Unsure of what happened and what to do, Ghoulia attempts to bide her time with other things until she can figure it out. As for the Time Portal lens, Sparky has set up his own laboratory elsewhere in the catacombs, unknown to anyone in the present, and is busy putting the finishing touches on his latest creation in the hopes that, with modern technology, he can succeed where he failed previously.
Outside the school, at the racketball courts, Avea has Frankie standing in a group with both her fused friends and the other hybrid students as Avea explains that she will pair each fusion with a hybrid student to help them get better accustomed to their fused form. When Robecca and Draculaura accidentally lose control of one of the thrusters on their feet, Avea thinks she's volunteering to pair off with her, much to Draculaura's embarrassment. With that, each fusion is paired off with a hybrid to learn from them: Clawdeen and Venus with Bonita, Cleo and Toralei with Neighthan, Draculaura and Robecca with Avea, and Jinafire and Lagoona with Sirena. At first, the fusions have a hard time with their abilities, but with time, effort, and patience, their training with the hybrids begins to pay off, and they are able to successfully gain control of their fused bodies, while also becoming good friends with the hybrids as well. Though Frankie is impressed by the training, she's still deeply concerned about her friends and their well-being. As she and Neighthan discuss it in private, a romantic relationship begins to blossom between them, only for Frankie to suddenly suffer another surge of electricity in her neck bolts, electrocuting Neighthan much harder this time. However, Neighthan points out that this is how he can tell she's alive because of all the energy she discharges from her emotions.
Soon, Sparky manages to finish his creation and bring it to life, but when he takes a celebratory iCoffin photograph of his success, the flash startles his creation, sending it into a frenzy.
Meanwhile, the time has come for Mr. Where's play to make its official debut, but it barely gets underway with Frankie and her fused friends before the performance is crashed by Sparky's creation in its frenzy. When Toralei and Cleo make the mistake of taking a picture of it, they only enrage the creature again, who then uses the Time Portal lens on its chest to capture them. After it then captures Jinafire, Lagoona, Draculaura, and Robecca, Frankie teams with Sparky and the hybrids to try and lure his creation back to his lab to shut it down. That's where the scenes from the prologue play out again with Neighthan tricking the creature with a fake Frankie painted on a casketball, Sirena angering it with her iCoffin, and Avea and Bonita lifting Neighthan and Frankie to safety. Together, they manage to lure the creation back to Sparky's lab, and Clawdeen and Venus manage to pin it down with their vines, but once the creature is hooked up to be drained of its energy, the effort fails, and Clawdeen and Venus are soon captured in the Time Portal lens as well.
That proves to be the last straw for Frankie, as she confronts the creation directly, voicing her anger and fury at what it has done to her friends. As she does, her neck bolts begin to glow and discharge more and more electricity. Neighthan realizes that its her spark of life being manifested by her strong emotions and compassion for her friends. Sparky realizes that is exactly everything his creation is not and Professor Hexiciah was right. With that, Frankie removes her neck bolts and places them back in inverted, before grabbing that severed ends of the cables in her hands. Despite a plea by Draculaura to not go through with it, Frankie angrily shouts, "Give me back my friends!!!", before connecting the severed ends of the cables to her neck bolts, allowing her electricity to flow from her into Creation 4.0, electrocuting it. As Sparky and the hybrids watch, Frankie soon begins emitting so much energy that her eyes begin to glow fiercely with it. Soon, the Time Portal lens reopens, and Toralei and Cleo are released. What's more, they have been defused and are back to normal. As Frankie continues, Jinafire, Lagoona, Venus, and Clawdeen are freed and defused as well, but the effort begins to take its toll on Frankie, as her stitches begin to pop from the strain, and she soon collapses in exhaustion. The freed ghouls plead with Frankie, telling her to stop while she still can as her body can't take much more, but Frankie refuses to give up until she saves Draculaura and Robecca. Calling on every ounce of energy she has left in her body, Frankie puts the severed cables to her neck bolts one more time, and gives it her all to save the last of her friends, and after a few tense moments, the Time Portal lens opens one more time, and Draculaura and Robecca are released and defused, before Creation 4.0 shows its battery having been drained, and shuts down for good, falling to pieces upon being touched by Sparky.
Tragically, the same is said for Frankie, as she collapses with only moments left to live as she used up all her spark to save her friends, her family. In her dying moments, Frankie encourages Sparky to not give up on his attempts to create life, knowing he's meant for great things, just like her grandfather, Victor Frankenstein. It's then that Sparky reveals his real name to be Victor Frankenstein, making him Frankie's grandfather, and Sparky is his nickname. Frankie is happy to have met her grandfather after all, before she finally, peacefully, passes away. Everyone is heartbroken over her death.
Some time later, as everyone continues to mourn for Frankie, Ghoulia suddenly realizes that they can possibly revive her in Hexiciah's old rejuvenation chamber. Sparky agrees, and with everyone's help, the rejuvenation chamber is rebuilt for Frankie, she's placed inside, and Sparky attempts to revitalize her. However, the effort fails, and as Sparky wonders what he did wrong, Hexiciah himself arrives through the Time Portal lens. Robecca gives her father a warm hug, and as Hexiciah is impressed by how Robecca will turn out once he's done building her in the past, he confronts Victor in regards to the lecture he was supposed to attend after class 200 years ago. Hexiciah is mostly here to bring Victor back to 1814 where they belong, but first notices that they need to bring Frankie back first. As Sparky explains where he went wrong trying to revive her, Hexiciah again reminds him that to create life, it takes more than knowledge, it takes what you have in your heart to succeed. When Sparky argues that Frankie used up all her spark, Hexiciah explains that it can't fully be gone as it exists in every living thing. It is only when as Draculaura mourns Frankie that a sudden burst of gold light eminates from her chest. Draculaura explains that she was thinking about Frankie when it happened, convincing everyone to think of the happiest memory of Frankie that they can think of to help bring her back. As they do, Ghoulia sends a text to the rest of Monster High to encourage them to help as well. With everyone in the school lending their support, the spark grows bigger and bigger, with Victor adding that final bit, before the spark is collected and sent into Frankie, changing her appearance physically as it is absorbed, but for a few tense moments, nothing happens.
As Victor looks to Hexiciah for support, and Hexiciah smiles warmly at him, a familiar voice soon asks if she missed anything, revealing that Frankie has been revived, to everyone's joy. After Victor mistakes taking full credit for Frankie's revival, Hexiciah activates the Time Portal lens to take him and Victor back to 1814. Frankie wishes her grandfather good luck in his future endeavors, and Robecca tells her father she misses him already, before the two time travelers return to their time period.
After that, Frankie and the others perform the play again, and after inviting the hybrids on stage to join them, showing they are among friends now, the play is a rousing success as Mr. Where, Abbey, Bloodgood, Manny, and many others in the audience give Frankie and her friends a standing ovation and cheer.
Frankie then recaps the events of the special, along with an epilogue of what happened to the hybrids, her grandfather, and her second attempt at her family history project for Mr. Rotter, as her parents came clean about everything, showed her the real family album, and Frankie got an "A" for her project. All's well it seems as Frankie passed her project with flying colors, Monster High has some new students in the hybrids, and as for Ghoulia, she was given Hexiciah's old workshop, where she attempts to use the Time Portal again, emerging from it now dressed like a prehistoric jungle person, and fighting off a dinosaur that had tried to follow her through before she forced it back in and shut down the portal, leaving her pretty satisfied with herself.
- In Volume 1's webisode "Totally Busted", Monster High was established to be 2000 years old. This was corroborated by "Talon Show". "Freaky Fusion" retcons this to the school being 200 years old.
- "Freaky Fusion" continues the storyline regarding Hexiciah Steam. He made his first animated appearance in "Frights, Camera, Action!", albeit as mostly a shadow, his full appearance finally debuting in this TV special.
- The memories the students have of Frankie refer to events in "Friday Night Frights" (Robecca), "Why Do Ghouls Fall in Love?" (Draculaura), "13 Wishes" (Gigi), and "Scaris: City of Frights" (Rochelle).
- The three students sitting in the highest row on the left are missing when Robecca stands up to do her presentation.
- Fawn is among the students waiting outside after Creature 4.0 chased them out.