Continuity mistake: After Todd Howard knocks out his opponent in the boxing match, the crowd immediately starts throwing cups of popcorn into the ring. The camera cuts to Todd cheering and then an overview shot of his opponent laying face down on the canvas. At that view you can see that there is no rubbish or popcorn or anything else in the ring. Then when the camera cuts back to a side view there is loads of rubbish and popcorn all over the place once again.
Other mistake: Near the end of the movie, in the mansion overlooking the water, James Woods is eliminating the bodyguards. As he shoots the one at the bathroom sink, blood sprays all over the mirror, but the bullet never breaks the glass.
Continuity mistake: Near the beginning of the film, the soldiers are filling sand bags with mud. Beletsky, whose hands and forearms are covered in wet mud, puts down his sandbag and takes out a photo of his girlfriend. In the next closeup shot of him holding the photo, his hands are suddenly clean and dry. (00:11:00)
Continuity mistake: When the angel lands face down in the pool, Michael Knight turns her over and her face is completely dry.
Other mistake: Despite the noise of the demon in the house, the tornado clouds outside, the flashing lights from the demon exploding and the fireworks in the sky - not a single neighbor is anywhere to be seen. Even after daylight breaks the neighborhood is a ghost town as we pan away from the actors.
Plot hole: The fact that Buddy placed the knife and note in the steering wheel of Jerry's car is unrealistic. Buddy first met Jerry in the bathroom after school started and Jerry hasn't gone outside of the school building to his car until this point later in the morning... so there's no way that Buddy could have known which car was Jerry's to pull this stunt.
Continuity mistake: The car in the garage moves from the parking spot to outside of the parking designated spots despite the car never starting. (00:05:10)
Continuity mistake: When Molly Ringwald is on the phone at the club and gets approached by the girl in orange, throughout the whole conversation the position of the phone receiver in Randy's hand is wildly inconsistent. (00:09:30 - 00:11:00)
Continuity mistake: When Donna and Taryn go to the restaurant, they are greeted by its owner Ashley. His hands change position depending on the camera angle.
Revealing mistake: There are times in the movie when you can tell Bobo's beard is fake such as when Penny's giving him a drink from a 7-11 and it's peeling off near his right ear.
Audio problem: A punch thrown by Big Eddie during her fight makes a sound before it's even connected.
Revealing mistake: Terri is replaced by a stuntman in a dark blond wig once she puts on her motorcycle helmet outside the hardware store.
Continuity mistake: During the scene when Bobby's auditioning for a part, there's a picture on the wall of Helen Martin (the lady playing Bobby's Grandma). The picture disappears and reappears during the scene.
Revealing mistake: A bunch of seedy individuals are gathered, weapons in hand. Unbeknownst to them, though, deadly ninjas are creeping by, with all the speed of fast-forwarded footage. The problem, besides how obvious the trick is, is that it also features a visible jump cut; you can see the foliage change position literally from one frame to the other during the same shot. (00:01:30)
Continuity mistake: When Frances takes Helen to sleep in the car, he puts her in the back seat from the drivers side. In the morning the camera is looking at her through the the window of the door on which she appears to be leaning. Yet when she gets out of the car later in the scene, there is a canvas draped over the door way.
Continuity mistake: Rick Latimer is at the bar with his buddies. He spots his ex-wife on a date with the divorce attorney and begins rambling. "This kind of sh. Happens", one of his friends says. The friend next to him, rightmost position, is smoking, and his hand is suddenly raised at the cut. (00:02:45)
Continuity mistake: When the pirates swears the oath to kill Dragon Mao, they drip blood on one of the pirate's hand. The blood stains on his hand differ between the shots. (00:02:50)
Continuity mistake: After the grocery store visit, Joan Jett walks to her room at the hotel and goes to her room on the second floor, a short time later she opens her room door which is now on the first floor. (01:35:00)
Audio problem: At the beginning, when mother and daughter arrive from New York, they try to find someone who can take them to the Sullivans'; while working this out, there is a man playing a guitar; in the beginning, everything's fine, but soon his hand movements don't match the sound.