Continuity mistake: When Rennie gets up and walks over to the closet, you can see some items on the side, such as a decorated silk cloth, a bag etc. When Jason then looks through the porthole into Rennie's room, the position of all the items are different. (00:21:35)
Continuity mistake: When Tim gets stabbed, the killer's silhouette shows that he's holding his knife overhand. When he stabs Tim, he's holding the knife underhand.
Continuity mistake: When Redferne finds the page of the Grand Grimoire, he is holding it with his right hand. In the next shot, he is holding it with his left hand. (00:52:17)
Continuity mistake: When Fuller falls to his death, the mannequin used as his stand-in gets decapitated on its way down. It even makes a loud noise. When Fuller lands, however, his head is still on his shoulders.