Jason shaves Josh's moustache before possessing him. No explanation is given.
According to the two-disk DVD set His Name Was Jason, which covers the making of the series over thirty years, it was an attempt to insert a homoerotic element in a series that (in the filmmaker's eyes) had a great double standard in its sexual exploitation.
The appearance of The Necronomicon from Evil Dead.
Perhaps the Necronomicon's appearance was a bit of foreshadowing?
Fight Scene Failure: During the final showdown between fully returned Jason and the protagonists, you can clearly see Jason preparing for the impact when he is about to be hit with a shovel by Steven.
Fridge Logic: Creighton Duke makes a considerable amount of noise about how "the only way" to permanently stop Jason is for a blood relative to stab him in the heart with a special mystical dagger that will banish him to Hell. However, it's not explained what would happen if, say, Jason's heart had been destroyed during the FBI's ambush along with the rest of his body. Or if the medical examiner had tossed it into an incinerator before it had a chance to work its mojo. Or, finally, if one of the people Jason possessed was captured and put into a thermite bath. Any of these things would result in Jason's physical body being destroyed as well as any chance of him hopping into a new one.
One of Jason's victims early on in the film is a girl who he stabs then rips in half with a pole. It you pause quickly before he rips her, you can clearly see that the girl was already sliced in half.
At the police station, Steven is shooting at Jason who was in Robert's body at the time and headshots him. Again, pause quickly and you can see a bullet hole already in Jason's head before he gets shot at.
After Jason gets stabbed with the dagger, agents of Hell sprout from the ground to drag him down under. The look of the hands...no. Reminds one of the giant foam fingers they sell at the sports games...
Squick: Jason tries to possess the body of his baby grand-niece. When that fails, he possesses his dead half-sister instead. Through her private parts.
Diana is the half-sister of Jason, who is hinted to know about his origins. But her role is just to die early in the film and have her corpse be conveniently present for the climax.
Since Jason is able to possess living characters, it should give him an opportunity to actually say something, anything, in adulthood, and it is squandered to a half-hearted attempt to trick protagonists.
Visual Effects of Awesome: The amount of makeup on Jason's regular body and the extreme damage his other bodies are put through are by far the most convincing special effects in the movie.