Continuity mistake: In the film Tommy tosses the alien mask that he wore to scare Reggie on his bed and the mask slides down the wall and is all crinkled up. In the following shots Tommy takes out another mask and you can see the alien mask now laying flat on his bed and away from the wall.
There are three different hockey masks used either in this film or its advertisements. The first is the one that the Jason impostor (Roy) wears. It has two blue triangles below the eyes. The second is the one the real Jason wears when Tommy sees him in the hospital room at the end, with the red triangles. The third is featured on the poster. It has an un-holy amount of breathing holes on it.
Continuity mistake: When Reggie finds the bodies in Tommy's room, Violet is first propped against the wall, but in the next shot, she is lying down, then she is propped up again.