Plot hole: In the first scene Alice hears on the radio that three teenagers had been murdered in Haddonfield just down the street from where they live. Yet a few scenes later, the sheriff finds out from his deputy that 3 bodies have been found. Wouldn't the police department know that before it made its way onto the radio news?
Suggested correction: When Alice is on the phone, she tells her friend she can hear the sirens so the police knew about the bodies. As for the sheriff, he'd been busy with Loomis all night. He might have heard about the bodies in the house but figured the other policemen could handle it and that way he could continue helping Loomis. The main reason the deputy came to talk to him, however, was to tell him that his daughter was one of the victims found.
Halloween II was a troubled production, and the scene with Alice was added during re-shoots. Note that the previous scene with Mrs. Elrod also includes a news report about the discovery of the bodies. I've seen no concrete evidence of this, but I've wondered if the scene with Mrs. Elrod was shifted closer to the start of the film, and was originally meant to take place after the scene with the sheriff.
Good theory, but the deputy runs up to the sheriff and informs him for the first time of all three bodies.
Plot hole: When Jason is in Ginny's cabin, she's under the bed seeing where he's at. So how did Jason manage to get up on a chair and wait for her to come out without her seeing him do this? She had to see him do that, but when she pokes her head out, she's surprised to see him there.
Suggested correction: She was a bit preoccupied with the rat that got up close and personal to her. She heard the creaking, but when she looked back, she didn't see him, assuming that the sound was made by him exiting through the cabin's door. The creaking was actually him getting up on that chair, but she wasn't looking at the door because the rat was in her face.
Plot hole: After the first murder in Pam's dorm room there should be blood everywhere but when Pam returns to change her dress there is only a single stripe of it on the bedsheets.