Continuity mistake: When Laurie runs away from Michael Myers in the boiler room, she climbs a window and falls into a storage room. Her hospital gown gets flipped as she falls, exposing her underwear. The close-up shows her falling again, this time without the upskirt shot.
Continuity mistake: Nurse Jill turns around before Michael Myers stabs her. After she's stabbed, she's already facing forward and her head doesn't snap to face the camera.
Continuity mistake: After Nurse Karen is drowned by Michael Myers, he drops her backward. The close-up shows however that she falls forward.
Factual error: At the end when Loomis lights the lighter, the room explodes and is engulfed in flames. Loomis would've burned to death quickly yet shows up in part 4 with burns on his face and arm.
Suggested correction: First, surviving an explosion is unlikely, but not impossible - there are plenty of real-life stories of people surviving fiery blasts. Second, I would argue that it definitely falls firmly under suspension of disbelief, and therefore I don't believe it's a valid mistake. And third, even if it was a valid mistake, this should be a mistake under the "Halloween 4" page, not the "Halloween 2" page.
Plot hole: Early on, the TV in the Elrods' house is showing a report (corroborated by the authorities) of three bodies being found in the Wallace house. However, later on during the Ben Tramer accident scene, the deputy rushes up to the sheriff to inform him that three bodies were found (including his daughter Annie).
Character mistake: When Ben Tramer's friends report him missing to the police, they describe him as being 17 wearing a mask. This is what leads Loomis to make a positive ID... on Halloween.
Character mistake: The coroner determines that the burnt body of Ben Tramer (still unidentified) must be young, based solely on the absence of fillings in his teeth. Nobody considers for a moment that it could be a 30-something with good dental hygiene.
Continuity mistake: The front door on the Doyles' house is different from the one seen in Halloween. You can see this when Dr. Loomis leaves the house in the beginning of the movie.
Continuity mistake: When Jimmy finds Nurse Alves dead on a stretcher and slips over in her blood pool, he hits the floor and there is a lot of blood on his face (especially near his mouth). A second later however, in an overhead shot, his face is clean. (01:03:25)
Continuity mistake: After Laurie wanders into a hospital room and unsuccessfully tries to use the telephone there are a series of shots cutting back and forth between the room and Laurie looking out into the hallway. In the shots from inside the room the telephone shifts position at one point. (00:59:01)
Continuity mistake: When Michael is stalking the hospital corridors there is a scene when he hides in the baby unit and is observing the Head Nurse berate Nurse Karen for being late again. The scene switches back and forth between a close up of the two nurses talking to a shot from Michael's perspective of them from inside the baby unit. In the close up the Head Nurse's body is facing Karen, from Michael's perspective her body is facing towards him on the other side of the nurse station. (00:30:20)
Other mistake: Jimmy the paramedic walks into the major surgery room to find Ms. Alves dead on the stretcher, the blood drained from her body. As he turns to leave he suddenly 'slips' on the pool of blood, falling back first and knocking himself unconscious. However the next shot reveals that the blood pool extends out to the doorway, so there's no way he could have crossed to the stretcher without slipping in the first place while entering the room.
Continuity mistake: After the guy in the hospital slips in the blood puddle he has some blood on his face and mouth that disappear between shots.
Continuity mistake: After Loomis and the police officer see the fake Myers they leave the car with the doors closed but in the open view they are open again.
Continuity mistake: After the hospital guard takes a look outside he checks the trash container which has inside a box with a big bloodstain which disappears in the next shot.
Continuity mistake: When the guard is checking the warehouse at the hospital he holds the flashlight differently between shots.
Other mistake: After Myers stabs the blonde nurse the scalpel is clean of blood.
Audio problem: When Loomis shoots Michael in the opening here his gun sounds different from the previous movie.
Continuity mistake: When Michael's shown falling off the Wallace balcony in the opening scene it's on the front of the house not the back. Clearly this is a different house. (00:02:31)
Other mistake: When Michael dips the nurse's head into the scalding water, her face starts to burn and her skin starts to peel. But, nothing happens to his hand that is also going in the water while holding her hair. (00:52:15)