Continuity mistake: The photo pinned beside the window changes in appearance and position during shots. (01:18:45)
Continuity mistake: When Jason comes smashing through the window at the end, to attack Ginny who is getting up from the cot, the camera angles are inconsistent with the attack. First he is lounging at her from behind, to grab her. Then his distorted face is suddenly at her left shoulder before he's even touched her Then she's looking back at him and screaming before his hands even touch her and pull her out of the window. (01:24:20)
Character mistake: Ginny is supposed to be put head first into the ambulance, not feet first. All the monitoring equipment is in the front of the head. (01:24:20)
Other mistake: The narration in the film's trailer incorrectly states, "On a June night in 1980, Friday the 13th, twelve of her friends were murdered." In reality, only eight people were killed then, including the killer Mrs. Voorhees, whom Alice herself killed in self-defense. Mrs. Voorhees was not Alice's friend.
Continuity mistake: When Scott gets his throat cut, blood pours out. Yet when Terri spins him around, there's no blood anywhere on him except a small amount on his shirt sleeves.
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: 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.
Suggested correction: We're not given a specified length of time between Vicki's murder and the time Paul and Ginny returned. He could have had enough time to hide Jeff and Sandra, but then they arrived as he was dragging Vicki down the stairs (you could hear them outside as we see this). We didn't see every closet or room, so the bodies could have been hidden anywhere.
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: When Sandra and Jeff sneak off to Camp Blood they walk right along the waterline with the lake on their left, yet after crossing the barbed-wire fence, the lake (in the background) is on their right; this was a mirrored image.
Continuity mistake: Jason drags Vicky down the steps all bloody, yet doesn't leave any blood on the steps.
Plot hole: While underwater all of those years, Jason didn't seem to age. He seemed to be a child when he grabbed Alice at the end of the first film. How could he grow up to be an adult after only five years, as Paul stated during the campfire story?
Suggested correction: Dialogue in the film hints at what actually happened, which is that the end of the first movie was some sort-of panicked dream/delusion Alice had, while the real Jason has been living out in the woods ever since he "drowned," and thus aged into an adult. (Whether he actually did drown and came back to life, or escaped and fled out into the woods because he was mentally challenged is up for debate.) It's admittedly shaky, but the movie does hint at an explanation, so I don't think this really counts as a mistake.
Other mistake: There is a lot of bad continuity over how many vehicles there are. First there is Jeff's truck then Ginny shows up in her car. Later Paul says they only have two vehicles when they decide who is going to the bar. Later we see Vickie go to her own car when she's looking for her hair brush, so that's actually three vehicles. But there are at least 15 people at this camp. There would have to be more vehicles somewhere.
Other mistake: When Jenny is hiding in front of the yellow car you can see the top of her head yet Jason doesn't see it.
Other mistake: Vicki enters the darkened cabin and flips a switch on a nearby lamp, to discover the power is out. But as she grumbles and crosses to another table lamp that is unplugged, she plugs it in, and suddenly the whole cabin lights up.
Revealing mistake: When Jeff and Sandra are in the woods, they bend down to examine a mangled animal. You can see that the animal has human teeth, not animal teeth.
