Continuity mistake: When Michael enters the Elrods' home and steals the knife, as he picks up the knife from where Mrs. Elrod had left it, there are several drops of blood that fall onto the lunchmeat, presumably from Michael's injuries from having been shot. A few seconds later when Mrs. Elrod walks back over to the lunchmeat and reaches for the knife and sees the blood, the droplet patterns are different.
Continuity mistake: At the end of the first Halloween, Loomis fires six audible shots from his gun (whether or not they all hit Michael is irrelevant). However, at the beginning of Halloween II, Loomis' gun can be heard firing off seven shots. Also the front view of the house from the first movie and second movie are two different houses. When Michael is shot he falls off the balcony which is on the side or rear. The second movie shows him falling off the front of the house. Different railings too.
Continuity mistake: In the credits, Michael Myers is said to be 23. However, the fact that he is supposed to be 21 in both films (because #2 took place directly after the first) is stated in both movies.
Continuity mistake: During the scene where Jimmy the paramedic finds Ms. Alves in the major surgery room on a stretcher with the blood completely drained from her body, while turning to walk out, he slips and falls back first in the pool of blood. Later, he finds his way to his car where Laurie had been hiding and attempts to get help. If you look closely, he still has the same shirt on, but it has no blood on it.
Continuity mistake: When the guy in the Myers mask is being chased by the Sheriff and Dr. Loomis, the guy is hit by a cop car which crashes into a van and causes an explosion. In an overhead shot you see the body fall on the hood of the car, but when Dr. Loomis gets a closer look, the body is pinned straight up against the car and burning.
Continuity mistake: Jimmy walks across a huge puddle of blood before finding Mrs Alves dead on the stretcher. When he slips and is unconscious, you can't see any footprints, not even near the door where he came in.
Continuity mistake: Dr. Loomis shoots out the passenger window of the marshal's car, but it seems to be intact in later scenes, like when the woman is outside using the radio calling for help.
Continuity mistake: At the very end of the first Halloween, Loomis' first shot hits Michael while he is struggling with Laurie. A few seconds later, he is staring down Loomis and breathing very heavily. At the beginning of Halloween II, the scene is reenacted to reflect the ending of the first movie, but here you cannot hear Michael breathing at all after being struck by Loomis' first shot.
Continuity mistake: After Jimmy slips in Ms. Alves' blood, his position changes between the side camera shot and the above camera shot.
Continuity mistake: Notice how Michael is taking/reacting to being hit by the bullets at the conclusion of the first Halloween - you see him writhe in pain, his hand shake and grab near his side, and his body contort and literally twist before falling off the balcony - a believable shooting death scene. When the scene was re-enacted at the beginning of part II, all Michael does is lazily walk backwards and fall off.
Continuity mistake: When Loomis thinks he sees Michael but it is actually a drunk Ben Tramer in a mask, he runs after Tramer and pulls his gun. Brackett sees this and runs out of his patrol car, slams the door, and stops Loomis before Loomis gets off a shot. A few seconds later though, the car door is now open in the background.
Continuity mistake: When Michael stabs Nurse Jill in the back with the scalpel and lifts her off the ground, her shoes fall to the floor. A few seconds later, they are rearranged differently on the floor.
Continuity mistake: When Annie's dead body is rolled out on the stretcher her dad pulls the sheet back and revealing her slit throat. After a brief cut to him, when it cuts back to Annie the sheet covers her throat.
Continuity mistake: After the explosion and Michael is walking on fire, you'll notice he is right next to the burning stretcher. Then they cut to a scene of Laurie hiding behind a water fountain. In the next scene of Michael, he is now about 8 feet behind the stretcher walking towards her again.
Continuity mistake: Near the film's climax, the marshall is shown walking down a hallway by a soda machine and reacts to Laurie's screaming. He then makes a turn around to go see what was up. Several seconds (and many screams) later, Michael crashes through the door and the marshall is still running down the hallway by the same soda machine.
Continuity mistake: In the original film, the pumpkin at the Wallace's house was very small and fat, but in this film (which takes place the same night) you can see when all the cops and reporters are at the house that the pumpkin changed in size and the face is different as well.
Continuity mistake: The balcony from which Michael Myers falls from in Halloween 2 is different than the original Halloween. You can clearly see a canopy over-hanging the balcony in the original, but in Halloween 2 the canopy is missing. It appears that Michael's body falls and lands in two completely different areas between the two movies.
Continuity mistake: When nurse Karen first enters the hospital and changes into her uniform, she's clearly shown putting on a dark belt (either black or brown). However, in her next scene with Mrs. Alves, as well as the scene where she's tricked into entering the hospital room to fool around with Bud, the belt is white.
Continuity mistake: When Laurie leaves the hospital, she exits out of the hospital doors. Somehow the doors stay open. Later on in the far away shot, the doors are closed, then they are open again in the next shot.
Continuity mistake: Towards the end of the film, when Dr. Loomis finally finds out Michael is at the hospital and orders the trooper's car to turn around. As the car turns around, the lighting outside appears to be pre-dawn however they arrive at hospital and it is still pitch black.