It's repeatedly hinted at that there are high tensions between monsters and normies. That alone doesn't seem so bad, more like a metaphor for racism and such. Then enter Van Helscream, a self-proclaimed expert of monster human relations. He's the one responsible for most of the tensions between monsters like vampires and werewolves, and everybody thought he was a hero for equality. The fridge horror starts to kick in when you start to wonder how long he's been at this, how many schools has he destroyed that were like Monster High, and even worse, what kind of damage he's done on the HUMAN side of things?
Apparently a lot of damage as seen in Ghouls Rule: the cop decides to give Holt "the trick or treatment." That might sound ridiculous, until they strap Holt into this rather creepy machine that looks like it's going to BEHEAD him! All for a couple of harmless pranks!
Valentine's love spell. In Why do Ghouls Fall in Love Valentine puts a spell on Draculaura to force her to fall in love with him. The implications alone are pretty frightening, but it gets worse when he reveals that if he doesn’t harvest her heart before three day’s time, she’ll lose her heart permanently. At first it seems more depressing than frightening, but then you realize that along with her ability to love, she’d also lose her compassion, her kindness, her mercy, and basically everything that makes her Draculaura, and possibly even turn her into a cruel and horrible person.
Not just that, a vampire without a heart is a vampire who would not turn down a chance to suck blood. In short losing her heart would have meant her pretty much becoming a killer...
Zombies are reanimated corpses. This means that Ghoulia, Slo-Moe and all the other members of the zombie population used to be normies- until they died and were reanimated as functioning corpses. Though whatever animated them seems to prevent body decay, they do still suffer from lessened mental faculties and physical reflexes(even considering Ghoulia's high intelligence, she is unable to actually speak anything other than the zombie "language" of groaning).
Frankie's made of body parts. Body parts of teenage girls; probably already dead ones, which means her father and mother had to go get them. In her diary, she says her father was yelling 'It's alive!' and that he believed kids needed a strong sense of tradition, so it's likely she was made the same way he was. So basically her mom and dad went around and stole from graves.
There is really a lot of fridge horror considering the doll's backstories. Like what made Draculaura go vegan to a point where blood makes her faint? Where did Operetta get those scars (very decorative scars too..)? What caused Spectra to become a ghost? And the fact that Cleo is afraid of the dark. And of course there is Robecca's story involving losing her dad because she missed a train ride home. When one thinks about it this line has quite an interesting, dark undertone to it.
A lot of people probably got mad at Gil for not trying to save Lagoona when she was captured, even if he did come back later to save the day, but if you think about it, he probably did the smartest thing any of us could of done: HE WENT FOR HELP! He knew that Lagoona's parents were nearby, knew that this was way too much for a couple of teens to handle, and went for help. And think of it this way: if he HAD tried to save Lagoona when he didn't, he probably would have ended up captured which would've meant that Barnum would've won.
Cleo de Nile, an Egyptian mummy, is a cheerleader. Cheerleaders form PYRAMIDS.
The Frankie and Jackson/Holt paring makes a lot of sense when you realize that they are both the results of extreme science and from Victorian literature.
Ghoulia being the smartest ghoul in school makes a lot more sense when you remember that, as a zombie, it means she has the mostbrains.