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.