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 (its made of rubber, or something like that).
Continuity 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.
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.
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.
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.
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.
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.
Continuity mistake: When Will and Lori are driving in the van you see a car's headlights behind them in a close up shot. However, in the previous wide angle shot, there was no car driving behind them.
Continuity mistake: In the fight scene on the pier, just after Freddy has sliced off Jason's fingers, Jason blocks the machete, Freddy slashes him with the glove and then cuts Jason's chest with the machete and raises the machete for a downward blow. They are now standing face to face. However, when Freddy makes this cut, Jason's back is all of a sudden turned, enabling Freddy to cut his leg from behind. There was no time for him to turn around between cuts.