Continuity mistake: Right before Jason slits Axel's throat, we see him grabbing Jason by his elbow. When it cuts from a shot above we see him holding Jason by his wrist. (00:13:25)
Continuity mistake: When Sam asks Sara to come into the water, Sara says no. Then Sam says "Then I'll go under water and stay there until you do", while placing her hands on the edge of the pier. When it cuts to a close-up of her she is resting her arms on the pier instead. (00:29:20)
Continuity mistake: When Trish is inching by Jason lying on the floor, in one shot she steps over his arm and her feet are near his shoulder, then in the next shot it shows her stepping over his arm again. (01:17:10)
Continuity mistake: When Tommy and Trish are hiding in a room, they sit down on the floor and Tommy grabs a chair in front of him. When it cuts the chair lies on the floor. (01:15:25)
Continuity mistake: In part 3, Jason was stabbed in the hand and leg yet there are no wounds or damage to his clothes.
Continuity mistake: When Trish drops the machete it falls half ways on a carpet. When Tommy picks it up it lays on the floor. (01:21:15)
Continuity mistake: This mistake is for the Deluxe Edition DVD only. In the previous film, Jason is defeated by an axe blow to the head, which pierces through the top of his hockey mask on the left side. In this subsequent sequel, the cut in his mask is still on the left side. However, for the menu of this DVD, the hockey mask is shown as the menu art with the same cut from the axe. However it's on the wrong side of the mask, being on the right side now.
Continuity mistake: When Trish and Tommy get to the house, it's pouring rain. When they get into the house, Trish's hair is completely dry and there's just a small wet spot on her blue shirt.
Chosen answer: He's not possessed. Dealing with Jason made him go crazy. In part 5, we find out he was in a mental hospital for a while, then gets sent to a home for troubled kids.