Antrum (also known as Antrum: The Deadliest Film Ever Made) is a 2018 horror film directed by David Amito and Michael Laicini.
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. The film is divided into two parts: an opening and closing frame narrative in the form of a mockumentary and a feature film. The documentary purports to tell the story of Antrum, a movie released in the late 70s that supposedly has deleterious effects on those who watch it; the bulk of the movie is made up of what is allegedly the only known print of Antrum, which has itself been altered by an unknown third party.
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. In 1979, a film named Antrum—shot in English but of apparently Soviet origin—is submitted for inclusion in a variety of film festivals; none accept it. Shortly after each rejection, the various festival directors die under suspicious circumstances. Several years go by during which the film remains unseen until it mysteriously appears at a theater in Budapest in 1988. During the screening, a fire breaks out, burning the theater to the ground; initially believed to be the result of a faulty projector, investigators later determine that audience members set the fire themselves. The film again goes unseen for many years until it is screened in a theater in California in 1993. Prior to the film, a concession stand worker doses popcorn with LSD; the combination of the drug and the film results in a riot during which a pregnant woman is killed. Following this screening, all copies of the film apparently vanish, and it earns a reputation as being cursed.

In 2018, a copy of Antrum surfaces, prompting a documentary crew to make a short film on its history and impact. Although the origins of the movie remain unknown, scientists and film experts who examine the 35 mm reel determine that, among other unique properties, the film utilizes disorienting sounds and subliminal imagery. The documentary crew further determines that unrelated, black-and-white snippets of film have been spliced into the original movie by a third party. The documentary pauses so that Antrum may be presented in its entirety for the first time in twenty-five years.

Antrum tells the story of siblings Oralee and Nathan, whose dog, Maxine, has recently been euthanized. After Nathan asks if Maxine went to Heaven, their mother informs him that because she was a bad dog, Maxine has gone to Hell. Traumatized, Nathan begins experiencing disturbing dreams and visions of demons. In an effort to ease his mind, Oralee claims to have obtained a grimoire from an imaginary classmate named Ike whom she claims is versed in the occult. Using the book—in fact, a sketchbook Oralee has filled herself with arcane drawings and "spells"—she takes Nathan to a nearby forest locally renowned as a place for suicides, telling him that it is the place where Satan fell to Earth when he was cast out of Heaven and that if they can find the place where he landed, the pair can dig a hole to Hell and rescue Maxine. Oralee guides Nathan through a series of rituals and "rites," intending all along to arrange for Nathan to discover Maxine's collar in the woods as a "sign" they have saved her soul. As the day progresses, Oralee is disturbed to find that her "spells" are having an apparent effect on the real world, conjuring actual infernal figures. Additionally, the pair accidentally interrupt a man attempting seppuku, and obliviously pass by the rotting corpse of a suicide near their campsite. Throughout their experiences, subliminal images of runes, pentagrams, and demonic figures flash onscreen; occasionally, brief clips of an apparent snuff film appear, depicting a nearly nude man and woman bound in duct tape and crying while an unseen