Revealing mistake: The roller coaster used for the Devil's Flight is really the Corkscrew at Playland in Vancouver, where all three movies were filmed. If you look during the opening credits, you can see the name "Corkscrew" up in the lights above the coaster. After this, it says Devil's Flight during the rest of the roller coaster scenes.
Continuity mistake: When Barris is served in the diner, french fries are scattered over his plate. When seen again, the french fries are replaced with vegetable sides.
Continuity mistake: After Eisenheim has disappeared, literally, from stage, Uhl and the policemen search his office. There, Uhl finds Eisenheim's notebook with the design of the locket in it. There is a large tear in the middle of the paper. It disappears when the inspector looks at it again after he has found the locket in the Prince's barn. (01:31:00 - 01:31:45)
Continuity mistake: In the scene after the bus rolls down (when they are at the beach), one of the girls is wearing a red bikini, but when she gets in the water it's black. (00:13:40)