Along with Robecca, the ghouls unlock Hexiciah Steam's secret lab under the school, where they accidentally find a time travel machine that takes them back to MH circa 1814. Here, Frankie finds the past versions of Victor "Sparky" Frankenstein (the man who made her parents and technically her grandfather) and Hexiciah Steam (Robecca's creator and one of MH's first professors). In Hexiciah's class, we learn past Victor is extremely gung-ho and sure of himself with regards to his science, yet in his zeal forgets the emotional aspect necessary for his work—and for a while has been attempting to learn how to create life. Later, Frankie finds Victor. Shocked by her creation, he relentlessly quizzes her on how she was made before she realizes she can't stay long. After Frankie assures him he'll know what to do, the ghouls return back through time—but the machine malfunctions and fuses them all together (save for Ghoulia). And Victor and Hexiciah follow everyone back.
- An Aesop: Family is more than where you come from; it's the people you love.
- Anti-Villain: Sparky endangers the lives of Frankie and the ghouls, but not out of malice. He only ever wanted a family of his own.
- Bittersweet Ending: Frankie and Robecca learn more of their heritage, Victor and Hexiciah are inspired to create them, and the hybrid kids finally find somewhere they know they'll be accepted—but Hexiciah is still missing and Victor is likely long dead.
- Butterfly Effect: Acknowledged by Jinafire immediately after the ghouls go back to the past, and ignored by Toralei, who the ghouls have to practically drag back through the portal (covered in past paraphernalia).
- Caged Inside a Monster: Sparky's robot at one point, traps the cast inside it's body, leaving Frankie alone to save them.
- Drama Bomb: With lots of backstory, the (kinda) return of Hexiciah, and the straight up Disney Death of Frankie Stein through saving her friends by destroying a robot with Shock and Awe? Oh yeah.
- Fantastic Racism: Before it was the monsters facing this from the humans, now it's about the hybrid monsters facing this from normal monsters. Thankfully, the students of Monster High are a lot more accepting than their old schools were.
- Heroic Sacrifice: Frankie uses up her life force to shut down the monster robot "Sparky" created. It's a Disney Death, but still.
- Hybrid Monster: The hybrids obviously, but some of the ghoulfriends end up fused as well, resulting in a dragon/sea monster, a werewolf/plant monster, a vampire/robot and a mummy/werecat girl.
- Mad Scientist: "Sparky", or the normie Frankie and the gang meet in the past. He follows them back to the present, believing he can unlock the secret to creating life by observing Frankie. He learns enough to create her parents later, which makes him Frankie's grandpa.
- No Equal-Opportunity Time Travel: Averted. A group of diverse monsters, both in monster races and real-world races, goes back to 1814 and the only problem they get is weird looks about their clothes. This can be handwaved by the fact that they are confined to Monster High the entire time and thus in an environment that was specifically created to be more inclusive than the general population.
- Pass Fail: It was established much earlier in canon that Lagoona is also a Hybrid, but this is never acknowledged in this film aside from her immediately showing the Hybrids sympathy and noting that it must be hard to fit in. Thus, one can conclude that she passes for a full-blooded sea monster at school.
- Stable Time Loop: Robecca leaves a note for her father while in his lab in the past. When he finds it moments after the girls leave through the portal to return to their own time, he is briefly puzzled by the note being signed "Love, your daughter", before then getting the idea to construct one.
- This is also the true motive of Frankie's parents when they sabotage her project by refusing to tell her about her grandfather. They know it'll send her back to the past and set the events of the story in motion, ensuring that they and she continue to exist.
- Token Human: Victor, while he attended MH. He's even made fun of for this by other students (some of which bear a striking resemblance to Clawd).