Plot hole: In the beginning, vampires are shown to be invisible in photos but then they seem to appear in videos like security footage and social media posts.
Plot hole: The camp tower scene and therefore the subsequent half of the movie are unnecessary. Dracula can fly and can drop Dennis from any height he deemed necessary. And it is not like they let Dennis make the decision to jump on his own accord, Dracula throws him off the tower. Also, it doesn't make sense for a heavyweight like Frankenstein to climb an unstable tower like that. So everything after Mavis becomes aware of the situation is avoidable.
Other mistake: When all the characters (Dracula, Frank, Murray, Wayne, and Griffin) all go to one side, the weight should make the tower fall down, but it didn't. However, after Dracula leaves and Frank goes to the other side, it happens to fall on his side.
Continuity mistake: Dracula has long vampire nails only when they mention them: when he tries to text and when he tries to fasten the belt on the car seat. All other times he has no nails at all.
Other mistake: If Bela can smell the humans from the castle during Denny's party, Vlad could easily smell Johnny as a human.
Suggested correction: On what basis? Bela is some sort of bat monster and Vlad is a vampire. Not to mention Bela has some strange idea that there are humans already and wants to find one to prove it. Vlad has no reason to suspect Johnny so he doesn't care anyway.
Other mistake: It is impossible for Mavis to fly from Usa to Transylvania in just few minutes and get to the castle at the same time that Drac and the others.
