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: 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.
Revealing mistake: In the beginning of Halloween 2, the scene where Dr. Loomis shoots Michael Myers repeatedly until he falls off the balcony is reenacted to reflect the events of the original Halloween. If you look carefully, you can see that the stuntman portraying Michael is actually walking backwards on a table until he haplessly falls off the balcony.
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.
Revealing mistake: In the scene where Marion is calling for help on the police car's 2-way radio, she speaks, "Marion Chambers with Doctor Loomis at the clinic; He's here." Right after that, the policeman on the other end of the radio starts to talk. However, Marion never lets go of the "talk" button on the radio's microphone, until the middle of the policeman's response to her request. You can't listen and receive anything on the radio while the button on the mic is pressed.
Visible crew/equipment: On the Goodtimes DVD release of Halloween 2, just after Dr. Loomis blows up the hospital room the camera switches to the hallway where Laurie is running away. The explosion comes through the hallway and you can see the right side of the hallway shaking - this shows that the wall is a studio set wall. You can also see wires behind it and the wooden supports that are holding it up.
Character mistake: The police claim the Myers house is at "45 Lampkin Lane." The address on the front porch clearly displays the number 709.
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: After Jimmy slips in Ms. Alves' blood, his position changes between the side camera shot and the above camera shot.
Character mistake: In the elementary school, Dr. Loomis spots Nurse Chambers and exclaims, "Oh, I hardly recognized you!" Although Nurse Chambers is wearing more make-up and is not dressed in a nurse's uniform, certainly Loomis would easily "recognize" a person with whom he shared an intimate, life-imperiling experience the night before, when Michael Myers stole their station wagon and fled the sanitarium. "Hardly recognizing" Nurse Chambers would have been a more appropriate response if the actual three year span between Halloween and Halloween II had occurred rather than the one night that was supposed to have elapsed between sequels.
Factual error: At the end of the film where the blinded Michael is swinging his scalpel aimlessly, it makes loud "swooshing" sounds. This is pure fantasy. I have personally mimicked what Michael did using similar small scalpels and even larger knives without almost no sound when swinging them.
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.
Revealing mistake: When Janet spins the dead Dr. Mixter's chair around, you can see his right hand flinch.
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.
Plot hole: Watch the scene where the drunk Ben Tramer (wearing a similar Michael Myers mask) was hit by the speeding cop car and then pinned against the parked van before burning. Even taking out the equation of accidentally hitting Ben Tramer, what was the cop car doing speeding at that rate of speed, head on towards a parked van on a side street? Remember, we only hear screeching breaks AFTER the car hits Tramer, and we never see the cop car swerve or any of that to miss hitting the van. Seems that even if Tramer hadn't been there, the cop car was sure to barge head on right into that van.
Revealing mistake: When Doctor Loomis touches the blood in the beginning, you can see a bit of material (it appears to be plastic) sticking to his fingers as he pulls them up from the grass. It appears as though it was somehow involved in the effect of him touching the blood. (Perhaps to keep it from soaking into the ground?).
Factual error: The films happenings are supposed to take place on Halloween of 1978, but the ambulance has rectangular headlights, which were not introduced on full-size Ford vans until the 1980 model year.
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: 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.