Deliberate mistake: In the jump scare at the end of the movie, the killer has both hands despite the amputation suffered earlier - however, since it's a confirmed non-sequitur dream sequence, it does not matter. (01:36:40)
Continuity mistake: After Barry has jumped into the water reclaim the crown, he comes out of the water with a perfectly clean shirt, but in the next shot the blood is back on his shirt as expected. (00:22:50)
Officer David Caporizo: Oh, and did this killer use his hook to cut all your hair off?
Helen: No, he used scissors, asshole.