Revealing mistake: When the guys are driving down the road, you can see Michael isn't under the truck. Yet 2 minutes later, he climbs in the bed. (01:16:25 - 01:18:10)
Continuity mistake: Rachel throws a couple of suitcases and Jamie throws 2 more and a sleeping bag down the stairs. Next shot shows a chair and boxes that were never thrown. (01:08:10)
Other mistake: In the scene where Jamie is in the closet, looking at a photo of her mother (Jamie Lee Curtis). The photo looks exactly like the scene where Laurie is sitting waiting for Annie on the ledge in the original Halloween, which wasn't photographed at the time, it's clearly a still from the movie.
Continuity mistake: Pay close attention to the scene at the end of the movie when Sheriff Meeker and several other troopers start shooting Michael. As the shots are being fired by multiple men, you will notice one of the troopers on the far left side of screen (blue/white flannel shirt, beard) lighting a stick of dynamite. As the shots pan back and forth between the troopers firing their shots and the shots hitting Michael, you will see this same trooper continue to keep lighting the dynamite. A few seconds later in the sequence while more shots are being fired at Michael, you will now see that same trooper now suddenly holding (and about to put down) a shotgun, the dynamite is now nowhere in sight.
Continuity mistake: When Dr. Loomis is thrown through the window by Michael Myers in the school notice that Myers' hair has strangely turned white. The next shot Myers' hair has gone back to being brown. This is more evident in the widescreen version. This was due to a reshoot. Originally the film was going to go with the white haired wig, but then changed to the dark hair wig. Obviously one scene was missed in editing.
Continuity mistake: Myers at the end rips Rachel's shirt on the sleeve when she is driving the truck, right after he rips it, it is together again, he rips it again, then it is together again.
Plot hole: When the deputy arrives at the sheriff's house, Michael gets out and leaves the door open. The deputy comes out to the car and sees it open. And he thinks nothing of it, despite knowing he didn't open it. Logic would say, "Well someone else opened it."
Continuity mistake: Rachel dumps a cup of coffee on Sheriff Meeker's daughter's white T-shirt in the kitchen yet there's no sign of a stain. It's not even wet.
Revealing mistake: When Michael sticks his thumb in the ambulance guy's head, you can see the inside of the fake hand.
Plot hole: Near the end of the movie, Jamie and Rachel are being taken down the highway to safety by the vigilantes when Michael climbs into the back of the truck from being underneath it. Michael then struggles, stabs, and violently throws two of the vigilantes from the truck, and the third vigilante, standing only inches from the other two and still holding guard in the back of the truck, appears to see or hear none of the commotion. Impossible, even for horror films.
Visible crew/equipment: When Loomis looks out the window for Michael, you can clearly see the cameraman's reflection (best seen on the Limited Edition DVD).
Continuity mistake: In the trick or treat scene, Rachel's purse disappears then reappears when she runs from Michael.
Plot hole: At the end of Halloween 2 Michael is completely engulfed in fire for several minutes. Even if somehow he was to survive he would be covered in scars. When we see him at the beginning of part 4 he has a few small scars on his arms. Same with Loomis, he has a few small scars on his arms and one on his cheek despite being in a gigantic explosion and fire. Obviously this was done so they could bring the 2 characters back but it still makes no logical sense.
Audio problem: Michael tears Rachel's sweater. The problem is it's not actually being torn, just sounding like it is. (01:19:50)
Visible crew/equipment: When Dr. Loomis arrives to the gas station the boom mic's shadow is visible on the ground. (00:19:02)