Revealing mistake: When Charlie turns and sees Michael after futzing with the garbage disposal, it's obvious that Michael's mask is a (rather poor) CGI creation. It looks very cartoonish and unlike the way it looks in the rest of the film. The scene was shot early in production with an original mask that eventually was tossed out for the final design when producers thought it didn't quite look right. Because Michael was in a medium-closeup shot and they didn't have time to reshoot the scene, they opted to (somewhat obviously) digitally replace the mask.
Revealing mistake: Joe is much too old to be in high school. He appears to be in his thirties (the actor playing him was 35 at the time).
Revealing mistake: When Alice and Claire land on top of the prison in the plane, Angel pulls a cable across the roof to help the plane slow down. As he pulls it tight the angle at which the camera is at wobbles due to the cable knocking it. (00:31:50)
Revealing mistake: When Kay-Em kicks Jason in the face during the fight sequence, you can see Kane Hodder's goatee. (01:03:40)
Revealing mistake: When the camera shows the coffee cup in the cop's car, you can see the ignition is in the off position. (00:09:16)
Revealing mistake: When the Headless Horseman is about to kiss Catrina's stepmother, you can see his actual teeth behind the filed ones. Christopher Walken's teeth are blacked out and their outline is visible against his tongue during the closeup of his face. (01:37:20)
Revealing mistake: Nearly at the end, the scientists find Alice's body at the waterfall, one of the men lifts up the cloth to take a look at her face. Her face is badly burned on one side and she is pronounced dead. However, take a look at the left side of her neck, you can see her either gulp or take in a quick breath of air. (01:19:05)
Revealing mistake: When Becky meets Simon in the cube, they hug, then Simon literally stabs Becky in the back. As she falls down to the floor, her black shirt reveals not only some of her chest, but part of a black microphone wire. (01:15:15)
Revealing mistake: Crash mats are visible on the steps, when the Father is thrown through the window and rolls down the stairs.
Revealing mistake: When Danny falls down from the ceiling, watch closely and you can see the security wire attached to his leg. (00:34:40)
Revealing mistake: When firing the crossbow, Van Helsing runs out of arrows, but the bow's canister is completely full of arrows. In the same shot the canister spins once and they all disappear. (00:25:55)
Revealing mistake: At the very end, a bat flying out of the mist toward the camera was intended to imply that Barnabas had taken bat form and could thus be around for a sequel. But through the haze, Barnabas can still be seen lying on the floor when the bat flies past. (01:36:25)
Revealing mistake: In the scene in which Jason kills the captain of the boat, it is quite obvious that Jason uses the blunt side of the machete to slit the captain's throat. (00:39:10)
Revealing mistake: After her brother's death, there is a scene in which Alice starts practicing with her brother's nun-chuks. They never show the real actress doing the tricks; instead, they cut to an angle from behind her and show a double who has darker, shorter hair than the real actress and is a bit bigger. (00:56:45)
Revealing mistake: When Toulon's puppet stage is set on fire, the flames in the foreground look rather like they are projected from a regularly set row of blow torches, rather than erratically flickering flames on a wooden floor. (00:25:05)
Revealing mistake: In one shot when Alice is in the shower, as she turns for the soap you can tell she is wearing brown underwear. (00:03:30)
Revealing mistake: When Karen and Whistler start to fire at Frost's men, after they discovered Blade's hideout, Whistler shoots a black guy who has a large bump under his shirt, quite obviously the squib. (01:11:00)
Revealing mistake: At the end when Norman is being stabbed at by Mary dressed up as Mother, Mary stabs Norman in the hand. You can plainly tell that this hand is a doll, as it is not a natural colour, it is stiff and is stationary, unlike Norman who is moving his hands. (01:35:10)
Revealing mistake: You can see the stick making the finger move when it's in the box. (00:38:20)
Revealing mistake: The "blower" on the yellow Firebird never runs. NO wonder he couldn't beat the Wraith. (00:44:10)