The tent that Judy and her boyfriend are camping in changes size between shots.
The video monitor and VCR on Dr. Crews' desk disappear as Tina looks at the picture of her father.
(at around 1h 13 mins) As Jason steps out of the puddle, his clothing is dripping wet. Then in the next shot, as he walks after Tina, his clothes can be seen as dry.
In Friday the 13th Part VI, the sheriff shoots Jason in the head through the mask, leaving a hole in the top of it from the bullet. In this film, the hole in the mask is gone, although the boat propeller damage still there from Part VI (the hole in the head of the mask) is not when it should be.
(at around 21 mins) When Eddie is reading stuff from his pile of paper, the pile is disordered. When the camera cuts to the pile, it is neatly stacked.
When Melissa comes into the kitchen asking where Nick is, Robin says "I think he went next door to visit Marilyn Munster." This couldn't possibly be an insulting nickname, as Marilyn Munster was the only normal one in the Munster family.
(at around 1h 16 mins) After Jason pulls the axe out of the tree stump, there is no cut mark left in the stump where the axe was previously stuck.
When Michael's car breaks down him and Jane are walking and Jane says Nick can drive us back to your car tomorrow. Michael asks how Nick would know where they are and Jane reveals she planned a surprise party for Michael and rented a great cabin.
In the next scene Tim is walking around the cabin cleaning up nonstop and complaining to his girlfriend that everyone was supposed to bring their own beer and his uncle was going to be pissed they drank all the beer in his cabin.
The rock that Jason is chained to in the lake is not the same rock he was chained to at the end of Part IV. This one is more cube shaped while the one at the end of the previous film was more flat and triangular.
(at around 1h 1 min) Cameraman's shadow on the wall just before Robin knocks on a door and says "Maddy"?
(at around 1h 3 mins) Reflection of crewman holding boom mic in the window that Robin passes by when she's alone in one of the bedrooms.
When Tina finds her mother's body in the woods, there's a close-up of Mrs. Shepard's face. At that moment, you can see someone's foot enter the frame at the top-left. It's either a crew member, or Jason was supposed to enter the scene.
When Jason is walking down in the forest, you can see three spotlights on the upper right.
(at around 52 mins) Cameraman's shadow on the side of the van when Ben is looking for Michael.
Jason is a corpse yet he can be seen breathing quite heavily in some scenes.