Revealing mistake: In the fight scene at the pier, after Freddy and Jason get thrown into the air by the carriage that smacks into them, they land on the pier in sort of slow motion. Watch Jason's left knee as he lands, you can see a kneepad.
Revealing mistake: When Freddy and Jason are fighting towards the end of the movie, Freddy cuts Jason's fingers off so he drops his machete. But when Freddy catches it you can easily see that it isn't a real one (it's made of rubber, or something like that). (01:20:40)
Revealing mistake: When Jason is slicing kids at the party, you can see the padding under their shirts
Plot hole: In the institute, Will's friend gets out of his room to get the guard's keys. He couldn't have gotten out of his room because there isn't a handle or door lock inside the room.
Revealing mistake: When Linderman dashes at Jason and impales him with an American flag, Will is dragging Lori (who is supposed to be unconscious). He's dragging Lori by her arms... but when he suddenly reaches behind his back with his right arm, her right arm stays up in the air. (01:13:50)
Continuity mistake: When Freddy and Jason get hit by the cart at the construction site, they land next to each other on the dock. But in the next shot, we see Jason getting up quite a distance away from Freddy. (01:20:10)
Visible crew/equipment: In the scene where Lori wakes up in the police station and follows the dropping blood, she turns a corner because she hears a little crying. Right after she turns the corner, the cameras show office windows. You can see someone sitting down and a cameraman on his knees.
Continuity mistake: In the boiler room in Jason's "dream", the container that pins Jason to the floor lands directly on top of him. However, in the close-up of it still pinning him down, you see Jason's upper-body sticking out to the side. (01:03:50)
Revealing mistake: When the drug "Hypnocil" is researched on the Internet, an article about the drug appears. If you pause the shot and read the article, you can see that it has nothing to do about Hypnocil. The article is about drug testing of students who engage in extracurricular activities. (00:55:10)
Revealing mistake: As soon as the drunk kid sets Jason on fire there's a few quick shots of Jason's face but there's a perfect hole right through his head where his eye is supposed to be and you can see the night sky through it. Some people say it's a reflection off the goggles to protect the actor from the flames. Either way it's a mistake. (00:40:45)
Plot hole: The sheriff orders a 24 hour roadblock on the town, yet the van has no trouble driving to Crystal Lake.
Continuity mistake: When the girls are at Lori's, just after Kia asks them if they think she needs a nose job, the lights flicker. When they flicker Kia is holding a compact in her left hand and she begins to close it. Both hands are up by her face but then the angle changes to a wider shot and her left hand is empty and on her lap and the compact is in her right hand as she places it on the sofa.