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.
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.