Revealing mistake: In the beginning when Michael crawls out of the mine shaft that was just bombed he floats downstream. You see that he floats up to the old man's dock. If you look at him you can clearly see that he is wearing a black lifejacket. The filmmakers didn't even try to hide it under his suit, it is clearly visible on the outside of his jumpsuit.
Audio problem: When Tina is in the car with who she thinks is her boyfriend but is really Michael Myers; watch her lips when she says the line "Nothing Mike, that's what I get, Nothing." It is obvious that this line was dubbed in over something else as her lips do not match that particular line. (00:42:55)
Visible crew/equipment: While Mikey is shinning his car (as well as the stage light already listed as a mistake), as he goes along the side panel, just before the side mirror goes out of shot you can see the camera go past and a guys head in the reflection of the mirror.