Other mistake: When Sheriff Tucker shows Pam the newspaper clippings taken from Roy's wallet, plainly two of three columns in the article are identical and have nothing to do with Jason. (01:21:35)
Plot hole: When the cop shows Pam the newspaper clippings they include what look to be fresh photos of the real Jason from the events of Part IV, yet no photographer is ever seen taking pictures of Jason alive in the previous films and most likely wouldn't live long enough to publish the photo. (01:25:00)
Plot hole: When the couple go into the woods to have sex, after they finish, the guy goes to a pond to clean up, which is not very far from where he left his girlfriend. A couple minutes later, "Jason" is about to kill her, and she screams very loudly. Despite this he doesn't hear her.
Continuity mistake: We see Vic outside the halfway house, just starting to chop a 4-foot log with a double-bit axe. In the same scene a few moments later, as Joey approaches, Vic has chopped about a third of the way through the log. Problem is, it's a completely different log (different shape, texture and color).
Other mistake: After noticing that Tina is dead, Eddie fearfully backs away and leans against the tree. You can see Roy put the leather up and over the tree. This is impossible. He would have to whip it around the tree, not over it.
Revealing mistake: During several of the deaths committed by the impostor, look closely. The shirt sleeves are dark green instead of the dark blue sleeves of the jumpsuit the impostor wears. Clearly Tom Morga, the hallucination of Jason, did these scenes instead of Dick Wieand, Roy Burns/impostor Jason.
Continuity mistake: As Tommy reaches Jason's grave, he hears laughter and voices coming from the woods. As the voices move closer we see lights in the clearing. Tommy runs off in the bushes to hide. Moments later, two guys with flashlights and shovels suddenly rush in, from the opposite left, instead of the clearing path at the right, from where they were.
Continuity mistake: When Lana is hit by the axe, it hits her horizontally, but in the shot of her corpse, it is shown vertically.