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.
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.