Other mistake: In the final scene of the movie, Megan starts a boat motor and uses the propeller to hit Jason in the face, who has been chained down underwater. But if Jason can only barely reach her foor from underwater, there's no way the boat propeller is underwater far enough to reach his face.
Continuity mistake: Jason kills Burt and takes his belt, but the belt appears around Jason's waist before he has the chance to put it on.
Continuity mistake: When Tommy throws Jason's mask in his grave, when Jason wakes up from the lightning bolt. Jason picks his mask up off the ground yet Tommy threw it in his grave.
Continuity mistake: When Jason stabs Cort in the head (Cort is driving the camper) we see an exterior shot of the camper before it flips over. Look inside the camper; Jason is no longer standing behind the driver's seat where he stabbed Cort. In fact, Jason is gone altogether.
Revealing mistake: When the counselors show up at camp with groceries, Paula and Cort walk away with bags to take inside. However if you watch the reflection in the side of the truck closely you can see them sit down and wait for the scene to end.
Revealing mistake: Near the end of the film, when Tommy and Megan are driving towards the camp, a shot is reused from the earlier police chase scene. You can tell by the reflection of the red police lights in the trees.
Continuity mistake: After Jason kills the 3 paintball players, he comes after Roy who panics and shoots Jason in the chest with a paintball. Jason even looks down at the paintball stain before he chases after Roy. Yet in all the later scenes, the paintball stain is gone.
Continuity mistake: When Jason kills Lizabeth, the first shot shows Jason with his feet on either side of her head, but in the next shot, his feet are together.
Visible crew/equipment: Camera visible in the bottom left of the window when Sissy pours the soda out.
Continuity mistake: In the film Tommy pulls the rod out of Jason and you see Tommy remove his right hand glove. In the next shot, Tommy is taking off the right glove again.
Continuity mistake: When Megan dives into the lake her hair is in front of her face but in the very next shot it's combed back.
Visible crew/equipment: When the RV flips over in one shot you can see a stage light in the darkness.
Continuity mistake: When the sheriff first drives into the camp, the red and blue lights on top of his police car change position from shot to shot.
Plot hole: After Jason is "shocked" back to life, Tommy gets into his grave and is trying to get the metal pole out of Jason. During this time, Jason is looking directly at Tommy while he's trying to get the pole out. And Tommy looks right at Jason a couple times, so he should know he's alive, But Tommy doesn't realize he's alive until he grabs him from behind.