Continuity mistake: In the beginning of the movie, Mavis stares at the window. When Drac sings to her, the window is closed in the first shot, but in the next shot it's opened. (00:01:00)
Continuity mistake: After Dracula wakes up from being unintentionally knocked out by Johnny, they find themselves at the top of a very high cliff. There are two shots featuring Dracula and Johnny with the entire cliff visible; in the second shot, as they are falling, Johnny and Dracula appear to have shrunk tremendously. (00:52:30 - 00:53:00)