Revealing mistake: When Ethel gets a cleaver in her face, blood spatters everywhere. Yet the cleaver blade is still clean. (00:56:35)
Revealing mistake: When Jason is raising the machete above Tommy in the woods, it's obvious that his eyeholes are covered with black cloth. This also happens at the end of the movie, where Tommy hallucinates about Jason in the hospital. (00:04:45)
Revealing mistake: When Anita lies dead on the ground with her throat slit you can see her pulse in her neck. (00:53:05)
Revealing mistake: When Demon is using the outhouse, his pants are unzipped but not pulled down. (00:53:00)
Revealing mistake: During several of the deaths committed by the impostor, look closely. The shirt sleeves are dark green instead of the dark blue sleeves of the jumpsuit the impostor wears. Clearly Tom Morga, the hallucination of Jason, did these scenes instead of Dick Wieand, Roy Burns/impostor Jason.
Revealing mistake: When Tommy is about to slice Roy's arm, you can see that he is not really holding the machete in his hand. (01:19:20)