Revealing mistake: When Jason is on top of Ginny's car, she reacts to the pitchfork through the roof a second too early. (01:10:50)
Suggested correction: She had just seen Jason through the window before he disappeared. Then the pitchfork comes the roof. Just before she screams, you can hear the pitchfork tearing through the fabric of the roof. That's what's she's reacting to.
Also, when you see the car and Jason is reaching in through the hole in the roof from the passenger side, it's pretty obvious she would have seen him before he stuck the pitchfork through. That could be another reason she react before we see the pitchfork.
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)
Visible crew/equipment: When Terri is back at the cabin looking for a knife, she crouches down giving us a clear view of the mirror. Look closely, you can see a crew member carefully moving in the right side of the mirror. (00:48:00)
Plot hole: When the counselors are dividing up who is going into town to the bar and who is staying, Paul tells them only a limited number can go because there are only two cars. They leave in a little bug-looking car and a pick-up truck. Then, when the girl is freshening up for the guy in the wheelchair, she goes outside to what is presumably her car, searches the front seat, and finds the hair brush she is looking for. I guess technically, there are only 2 cars and 1 "truck" but the truck is the other vehicle that goes into town, so presumably he meant 2 "vehicles" which would be incorrect since a 3rd was obviously left behind. (00:42:15 - 00:57:15)
Continuity mistake: When Ginny shows up at the campgrounds late, as she gets out of her car to go speak with Paul, she pushes the driver-seat sunsheild down. After their talk, she goes back to the car and the sunsheild is up. (00:20:35 - 00:21:55)
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: When Jason sneaks up behind the cop and raises the hammer to whack him, the angle shows it aiming for the cop's neck, but in the continuing shot, he strikes the back of the cop's head. (00:45:35)
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)
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.
Character mistake: Ginny should've been loaded head first into the ambulance, not feet first.
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.
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.
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.
Revealing mistake: Notice when Jenny pees it's shown just pouring out. But she's lying flat and her jeans would obviously absorb most of it. But it just pours out like she's standing up with no jeans on. (01:14:30)
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)
Continuity mistake: When Jason takes the spear, he tosses the mask down, on the fifth step up. Later, when Vicky goes upstairs, the mask is on the sixth step up. (00:59:25 - 01:01:50)
