Other mistake: After Michael kills Laurie at the beginning, he hands the knife to the inmate with the clown mask. The next kill is the cameraman for which he uses the tripod ends. A few scenes later they show Michael standing holding a knife with fresh blood on it. He hasn't killed anybody with this knife yet so where did the blood come from?
Plot hole: When the first security guard, who stayed back to get something to eat, hears something in the laundry room, he walks over to the washing machine where he finds the head of the other security guard inside. He turns around screaming and trips over the security guard's body on the ground with no head. Wouldn't he notice the dead body on the ground when he first entered the room?
Continuity mistake: When at his house, the first crew member Michael kicks with a camera. He puts that camera on the ground, tripod closed and laying down. When the people first walk into the house they switch to a camera view that's up the stairs and you can see that the camera that was laying on the floor is now propped up against the wall.
Audio problem: When Myles is at the party in the office checking out the web broadcast, a guy and a girl bust in and intend to have sex there. What we hear the guy say doesn't match up with his mouth movements.
Continuity mistake: Freddie is stabbed rather harshly on the shoulder but there is no blood anywhere on his shirt or anywhere near his wound.
Factual error: The bandages for Freddie's stab wounds are on top of his shirt. If he were really stabbed severely three times on the shoulder, the paramedics would have at least make him take off his shirt to better dress the wound. Freddie didn't even take off his jacket!
Visible crew/equipment: At the beginning, when Michael kills the first security guard in the basement, just before he dispatches the second one, you can see a crew member's arm reflected in a window hitting the light shade to keep it swinging.
Continuity mistake: In the scene when Sara is looking through the bedroom closet the mannequin with the mask on falls on her and the head falls off but when Rudy comes in and lifts the mannequin back up the head is attached onto it.
Continuity mistake: At the party, when someone screams out to turn the volume down, right behind the kid that plays Decker is a blonde haired boy with a red smoking jacket. It then cuts back to inside the Myers' house for a few minutes. When it cuts back to the party that same blonde haired boy just walks in as if he wasn't in there before, asking what they are watching.
Continuity mistake: When Donna puts her shirt on after messing with Jim, she doesn't put her bra on. After Michael kills her, her bra is back on.
Plot hole: The nurse mentions that Laurie Strode is a potential suicide risk. With that risk, added to her mentioned escape attempts and being found on a rooftop, as well as being the prime target of a serial killer still on the loose, shouldn't she be under 24 hour protective watch?
Plot hole: When Michael kills Rudy all of his knives are now gone but when he chases Sara around the house he has another knife with blood on it. Where did he get the other knife from?
Continuity mistake: When Michael Myers is walking towards his sister's room at the mental ward, the camera shot is behind him, as he holds his knife by his side. The camera angle changes to his front, and now the blade is at his front.
Continuity mistake: When it flashes back to how Michael Myers survived the end of H20, we see the paramedic that he subdues and switches places with. That paramedic had a bit of a stomach on him, yet the figure of Michael Myers throughout the rest of H20 after the switch remains the same as the real Myers. [A side note: Halloween H20 WAS intended to be the absolute final film, but popular demand forced a return and obviously they needed a scapegoat excuse to bring Myers back. Still...]
Audio problem: When Donna runs into Michael in the sewer, she screams, but we hear the words, "Oh, shit."
Continuity mistake: When Freddy arrives at the Myers' house the sliding door at the side of the car is left open but after Sara sees Michael Myers at the window the door is shut.
Revealing mistake: When you see Freddy's car parked outside the Myers' house when the trunk is open,you can easily tell that the background is artificially created and there is a wall at the side with painted clouds.