Revealing mistake: When Jason breaks his hand through the door it's really strange how his hand makes a perfect square on the broken door. Telling that the door was already broken and then repaired loosely for the stunt.
Continuity mistake: In the film Jason kills the guy in the sauna with a hot coal into his stomach, and there's no blood. When Jason leaves you can see the guys chest and now it's covered with blood. (00:28:45)
Factual error: When Rennie and Sean are on the ladder and the toxic waste is flooding through "destroying" Jason, they are completely unscathed. There is no way there would be no splash back burning them, plus the fumes from the toxic waste which they are subjected to would have done them serious bodily harm.
Continuity mistake: Crystal Lake goes from a lake surrounded by land in previous installments to suddenly having the space for a small yacht and a channel that feeds right to the open ocean.
Revealing mistake: When Sean and Rennie run through the two glass doors leading down into the New York subway system, you can see Jason's shadow on the wall as he stands off camera and waits for his cue to walk on screen and kick his way through the glass doors. (01:19:25)
Continuity mistake: When Rennie and Sean are on the ladder in the sewer Rennie's position changes between shots. (01:29:50)
Revealing mistake: During the part where J.J. goes down to the boiler room to play her guitar, Jason sneaks up behind her. She screams and runs down more stairs, and then right before Jason kills her, as he lifts the guitar to hit her, in the lower right hand of the screen you can see the blood coming out of the guitar before it hits her. (00:21:25)
Continuity mistake: Rennie's visions of Jason as a boy change their appearance constantly throughout the film. At some points he is bald and deformed, much like how he was in the original film. At other times he appears as a normal, non-deformed boy with a full head of brown hair. At some moments he even appears as a mix of both (with a deformed face, but a full head of hair). This inconsistency is never explained or even acknowledged.BKAllmighty
Factual error: When Jason pushes Julius overboard, he would have drowned within minutes. No one can stay underwater that long without drowning.