Continuity mistake: When Jason surprises Vicky in the bedroom death scene. Jason pops out of the bed and his bag that he wears on his head is tied up. Then when they cut to Jason lowering his butcher knife, his head bag that he wears is un-tied. (01:02:20)
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.
Continuity mistake: When Jason slits Scott's throat, he slits straight across, yet the wound is diagonal. (00:48:25)
Revealing mistake: Just after the scene where Mark is killed, there's a shot of Jason's feet as he opens a screen door and walks across a dusty hardwood floor. As the dolly pulls backward across the floor, you can see the camera's roller marks in the dust. (00:59:10)
Plot hole: Jason drags Vicky's body down the stairs. A minute later, Ginny and Paul come in the house and see nothing. Jason even has time to hide Sandra and Jeff's bodies by the time Ginny and Paul go upstairs. Not possible in a two minute time frame.
Other mistake: When Jeff and Sandra sneak off to look at Camp Blood, they come across a dead animal. While they're bent down looking at it and have their backs to the camera, the cop for some reason sneaks up behind them and puts his hand on Jeff's back. The camera angle changes and you see the police car parked just off to the left with its red light flashing. There's no way that Jeff and Sandra would not have seen and heard the police car when they came up on the dead animal - it's almost right in front of them.
Continuity mistake: Jason drags Vicky down the steps all bloody, yet doesn't leave any blood on the steps.
Continuity mistake: When Jason enters the cabin you can see an umbrella. Yet when Vicky comes in, she's using that same umbrella. (01:01:35 - 01:03:50)