Continuity mistake: During the final chase scene where Melanie Kinnamin is running through the woods the pink sweater which is over her shoulders disappears and reappears at random, until she finally loses it by the tree where her co-worker is found murdered.
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.
Plot hole: At the end when Tommy is in the hospital, he gets out of bed and goes over to the drawer where his belongings are. He opens the drawer and there's the mask the killer was wearing. How did it get there? The police should have taken that as evidence. There is no way that police would let Tommy keep this mask for a souvenir.
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).
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.