If “Best Worst Movie” were revealed to be a complete farce one day, impeccably acted by the cast of “Troll 2,” I wouldn’t believe it. What I find even harder to believe is that the cast and crew of “Troll 2” — a 1990 straight-to-video horror film with a Rotten Tomato rating of zero percent and a seemingly permanent place in Internet Movie Database’s bottom 100 films — are passionate, serious and, above all, insane.

“Best Worst Movie” is a documentary that follows the cult classic “Troll 2” and its fan base. The subject matter is limited, and all the information given in its 90 minutes could have been delivered succinctly in 20. It’s a good thing, then, that the film is structured more like a comedy than a documentary — you’ll be doing a lot more laughing than thinking.

The film introduces us to George Hardy, an actor-turned-dentist who played the role of the dad in “Troll 2,” while he is making himself a protein shake in his comfortably sized Alabama home. Hardy has found a career in dentistry, but the resurgence of the cult following of “Troll 2” has reignited his interest in acting. He is the main subject throughout the film, and we are introduced to past co-stars, the fan base and conventions through his eyes. There is a reason for this: He is the most sensible person in the entire production. The rest of the cast is too delusional to fit even within a Christopher Guest film. Mental patients, a crazy cat lady and brainless megalomaniacs — you name it, “Best Worst Movie” has it.

It would spoil the experience to reveal too much about the rest of the cast, but there is one character who is especially exemplary of the film’s (unintentional) comedic genius. Don Packard, who played the drugstore owner in ”Troll 2,” is revealed to have been a mental patient who played his role in the film a week after leaving the asylum. He claims to have really wanted to harm the child (played by Michael Stephenson) in the film and delivered his lines not as an actor but rather completely convinced of his role because of his mental state.

In text, this all seems a bit tragic, and the same can be said of all the lives that surround “Troll 2.” Even Hardy, introduced as a fun-loving dentist, becomes a profiteering hack by the film’s end, going door-to-door in Alabama’s ghettos telling residents to attend his film’s local screening because “It’s the best worst movie ever!” Yet, in execution, there is comedy to be found in all of this tragedy. It recalls “American Movie” more than any mockumentary: The tragedy is all too real, but the laughs are even bigger because of it.

Grade: A