Continuity mistake: When Dr. Jekyll sits down to try his formula for the first time, he removes his ring from the ring finger of his right hand and puts it on the table next to him. After drinking the formula, as his transformation into Hyde starts, his ring is back on his ring finger.
Continuity mistake: During the final battle between Boone and Decker, at one point, they are wrestling on a wooden bridge, and the board beneath Boone's head breaks in half and falls into the cavern below. (It is even highlighted in a very dramatic shot looking downwards over the whole cavern as it falls) Yet, a few shots later, the board has suddenly re-appeared beneath his head, unbroken.
Continuity mistake: Norman pours poison into the pitcher of iced tea. In the next shot, we see him carrying the pitcher and two full glasses on a tray - but the level of liquid in the pitcher hasn't changed, even though he's supposedly filled the glasses from it. Later, when the pitcher is sitting on Mother's dresser, the pitcher's level is lower, but no one has poured anything from it. (01:00:05)
Continuity mistake: When the zombie Barry falls on Jordan, he's played by an obvious stunt double who isn't wearing any zombie make-up.