A drolly deadpan horror comedy done in mockumentary style, “TrollHunter” is the best giant-monster movie since “Host.” It’s a genre that Hollywood once excelled at, but now foreign filmmakers—from Korea to Norway—have clearly taken the lead.

Andre Ovredal’s cunning script is based on an admittedly ridiculous premise that’s nonetheless presented with such tongue-in-cheek matter-of-factness that you’re willing to swallow it for the duration. It’s that the gruesome creatures of Scandinavian folkore that live beneath the earth are real, and that the Norwegian government has secretly segregated them to isolated areas to avoid panic, using cover stories about bears and tornadoes to explain the times when they escape and wreak havoc.

Of course the picture reveals this gradually, beginning with a trio of college film students—glib narrator Thomas (Glenn Erland Tosterud), sound woman Johanna (Johanna Morck) and cameraman Kalle (Thomas Alf Larsen)—doing a documentary on a spate of bear poaching. In the course of it, though, they spot a furtive loner named Hans (Otto Jespersen), whom they take for the poacher. He initially tells them to get lost, but eventually reveals himself as the long-time enforcer of the TSS (or Troll Security Service), charged with tracking down and disposing of renegade trolls. The trio then tag along with him to record his exploits at a time of a peculiarly widespread outbreak of troll activity—the cause of which is revealed at the close.

This is all pretty absurd, of course, but Ovredal pulls it off not just by presenting it in the form of the footage supposedly taken by the kids (titles at the beginning inform us that over two hundred hours of film was anonymously deposited, and after authentication was trimmed to its present length) but by establishing from the first a dryly straightforward tone. That includes the characterizations. Tosterud and Morck are entirely convincing as a couple of callow but obsessed college types, with the former standing out for his wry on-screen looks of bemusement. And Jespersen makes the title figure a typically overworked cog in the bureaucratic machine, a fellow who goes about the job he’s done for so long doggedly but without enthusiasm while complaining of the poor working conditions he has to endure.

Jespersen also serves as the source of information about trolls, telling the filmmakers (and us along with them) of the various types and their habits and nonchalantly using the methods and weapons he’s perfected over the years to track and eliminate them. The background he offers wittily incorporates many of the elements of Nordic myth, including the creatures’ inclination to turn to stone (or, alternately, explode) when exposed to sunlight and their ability to sniff out Christians (a particularly amusing moment comes when Hans attracts the monstrous hulk in the culminating confrontation by putting a recording of “What I Friend We Have in Jesus” on his truck’s speaker system; there’s also a query about whether they’d smell belief in Muslims, too).

Ovredal doles out this data cleverly (and with an occasional wink), and he doesn’t disappoint when it comes to showing the trolls, either. As was always the case with the giant-monster movies of the fifties, the first appearance is just a glimpse, but soon the beasties are featured in full figure in sequences of considerable length, some of which are genuinely suspenseful (like one set in a cave where the humans are trapped), though not conventionally frightening. And the combination of visual effects (supervised by Oystein Larsen) and animation (supervised by Nina Bergstrom) doesn’t make the mistake of trying to convince us of its realism; the trolls are fashioned (by Havard S. Johansen, Ivar Rodningen and Rune Spaans) as though they’d stepped from the pages of books of fairy-tales, and presented in hazy light that gives them a magical appearance.

It’s that combination of down-to-earth earnestness, horror movie convention and understated humor that makes “TrollHunter” so enjoyable. By cunningly but stylishly mimicking the on-the-fly appearance of documentary footage Hallvard Braein’s cinematography fits the conception perfectly, as does Per Erik Eriksen’s canny editing, which manages to seem haphazard while actually showing a delicate control. Mention must also be made of Baard Haugan Ingebretsen’s sound design, realized by Andreas Revheim, which adds enormously to the impact.

“TrollHunter” is a sly, cheeky movie that shows how an old genre can be successfully resuscitated when approached with imagination rather than just a big budget.