Satan's Little Helper

Douglas "Dougie" Whooly is a nine-year-old boy obsessed with a video game, in which he plays Satan's little helper. His sister Jenna comes home from college for Halloween, but things turn sour when Dougie finds out she brought her boyfriend, Alex, with her. After a fall out with Jenna, Dougie wanders off and finds a man dressed in a cheap costume arranging a dead body on his lawn as if it were a decoration. Dougie naively believes the man is Satan, and asks him for help in sending Alex to Hell, which "Satan" nods assent to. In the meantime, Alex comes up with the idea of bonding with Dougie by dressing as Satan for Halloween. When Dougie comes back home, he tries to lure Alex into the basement where Satan is waiting for him, but fails. Dougie ends up changing plans to instead have Alex ambushed by Satan while he and Alex go out shopping for a Satan costume, where Alex ends up being left for dead. Dougie brings Satan home, whom everyone believes to be Alex. Despite Satan becoming forcefully, physically intimate with Jenna and his unwillingness to speak, Jenna interprets these as Alex's devotion to his Satan costume. When Satan and Dougie leave to get Halloween candy, they end up shoplifting a market for candy and tools, where Satan subsequently kills a bagger who tries to stop them and the two engage in a brief physical assault spree with their shopping cart. On the way home, Satan engages in a combination of assaulting and killing several more people, including Alex's estranged dad, before he and Dougie are accosted by the police. Satan indicates to Dougie to run home while he confronts the police, who are later found to be dead. In the meantime, it is revealed that Alex has survived, who finds out from a babbling man that all the police on the island are dead and the police station is on fire. When Dougie comes back home, he tells Jenna about what he and Satan have done. Still thinking that it is Alex in the Satan costume, Jenna begins to think that Alex is pushing the game too far. After he comes home, his new personality starts to frighten her, she realizes he is not Alex. Dougie's father comes home, and Satan murders him. He kidnaps their mother, which makes Jenna and Alex go after him, only to think it's Alex's dad who is responsible, but are tricked by the killer repeatedly changing costumes and putting his old one on a victim, including a Jesus costume to trick Dougie into letting him into the house multiple times by saying that it is God coming to save him. In the end, Jenna and Mrs. Whooly accidentally kill Alex and are left at home with Dougie and a police man, who is actually the Satan Man, who spray paints a 6 on their home beneath their address, 66, turning it to 666. As he enters the house Jenna wonders why he doesn't speak, with Dougie saying it's so Satan doesn't hear him.