Hell House LLC

On October 8th, 2009, an unexplained tragedy occurred at "Hell House", a haunted house attraction in the town of Abaddon, Upstate New York, in which 15 people, including nearly all of the staff, died in what authorities declared a "severe malfunction".
A documentary crew investigating the tragedy, led by producer Diane Graves, interviews people familiar with the case and finds rumours of something supernatural behind the tragedy. The crew tracks down the sole surviving Hell House staff member, Sara Havel, who provides them with uncut, behind-the-scenes footage that Hell House staff shot up to the tragedy.
Sara's tapes document the company's arrival at the dilapidated Hotel Abaddon in Rockland County, New York as they set it up for Halloween. CEO Alex plans the attraction's layout to culminate in a scene in the basement of an actress chained up, about to be sacrificed to a cult.
They hire several local scare actors, including Melissa, who shares with Alex and cameraman Paul that the hotel is rumoured to be haunted. Their expert interviews give the documentary crew further context. The Hotel was originally constructed by alleged cultist Andrew Tully, who chose the location based on the town sharing the name Abaddon with a demon who guarded the gateway to hell. In 1989, two guests went missing while staying at the hotel: an 11-year-old girl and her mother. Though Tully was cleared of their disappearance, the hotel's reputation was ruined, and Tully hanged himself shortly after.
As they set up the house, the Hell House team begins capturing supernatural events on camera, such as a clown mannequin moving on its own, shadowy figures appearing and disappearing during strobe light tests, and Paul and Sara being possessed. Despite this, Alex is determined to open the attraction on schedule.
As the haunting escalates, Paul considers quitting despite his loyalty to Alex. Later that night, Paul goes missing after being assaulted by a ghost girl. The next day, the crew finds Paul in the basement in a fugue state. Tony, the staff technician, quits after an increasingly delusional Alex continues to push forward. However, Mack convinces him to stay for Alex's sake.
Hell House opens to a large turnout. However, things quickly go awry as the audience learns the tragedy's origin. In the basement scene, Melissa is suddenly and brutally killed by a shadowy ghost cultist, causing a stampede of guests. In the chaos, Tony is killed trying to save Melissa. Mack and Sara find each other in the panic and flee to the attic, where they find Alex hanged. Sara flees as Mack is surrounded and killed by shadowy ghost cultists, cutting out the footage from 2009.
In the present, Sara asks for a break from the interview. She tells Diane she will be in her hotel room, room 2C. She suggests the crew enter the Abaddon Hotel to see the crime scene. Soon after, Diane and her cameraman attempt to leave a message at the hotel reception desk for Sara, but the receptionist informs her that no one under Sara’s name is registered as a guest and that there is no room 2C at that hotel.
Diane and her cameraman decide to visit the Abaddon Hotel site. Mitchell, a member of the documentary film crew, stays behind to catalogue Sara's footage. He discovers footage after Mack is killed, where a possessed Paul kills Sara before slitting his own throat.
Diane and her cameraman break in and see the aftermath of what unfolded that night while ignoring Mitchell's calls. They go to the second floor, where they see a room labeled '2C'. When they enter the room, they find Sara sitting with her back to them. Diane and her cameraman try to flee but are attacked by a ghoulish Sara and two other shadow cultists.