Violations of canon
That is, inconsistencies with earlier Universal films.
First, Dracula's well-documented mirror appearance. Odd thing about that, it looked like the director had taken pains to avoid the mirror, until the very end of the scene.
Second: The Title. Chick and Wilbur never meet Frankenstein - they meet his creation. Wilbur calls the Monster Frankie at one point.
Third: McDougal was bitten by the Wolfman, so he should turn into a werewolf at the same time Talbot does. (Three full moon nights in a row?)
"Well, there it is."