"Well, I suppose at your age you don't get krampus anymore."

Goodness knows there’s no shortage of Christmas movies, but we could use a few more Christmas horror movies, don’t you think? (Rhetorical question. What you think doesn’t matter.) The juxtaposition of merry and scary — look, they even rhyme! — is irresistible, offering a huge variety of devious possibilities that only a handful of memorable films have explored. “Krampus” may not become a perennial favorite on the order of, say, “Gremlins,” but it makes the effort with fiendish gusto.

We are spending Christmas with a typical American family, consisting of Tom (Adam Scott), Sarah (Toni Collette), teenage daughter Beth (Stefania LaVie Owen), and younger son Max (Emjay Anthony). German grandma (Krista Stadler) lives with them, and Sarah’s sister (Allison Tolman), her boorish husband (David Koechner), their bratty kids, and cranky old Aunt Dorothy (Conchata Ferrell) have arrived to make things worse.

Max is having an especially rough time. He still believes in Santa, for which his cousins tease him, and he’s been naughty lately. Crying bitterly, he rips up his letter to Kris Kringle and throws the pieces out the window to be carried away by the cold December wind. But as we know from “Mary Poppins,” torn-up letters from children tend to bring unexpected visitors who have dark magical powers.

The next morning, Christmas Eve, a blizzard knocks out all the power and phone service. When Beth goes to see her boyfriend a couple blocks over, she never comes back. The husbands, timid Tom and gun-toting Howard, go looking for her, while the rest of the family hunkers down in the front of the fireplace before being alarmed by noises from upstairs. At that point, all hell breaks more or less loose.

Krampus, a sort of malevolent Santa Claus who comes to punish bad children, is a folkloric character in the German-speaking world (where else?), hence the presence of German grandma to explain it. (Her story, shown as a stop-motion-animated flashback, is coldly beautiful.) “Krampus” doesn’t bother much with the mythology, which 1) keeps us from guessing what’s going to happen unless we’re already familiar with Herr Krampus, but 2) sometimes makes the action unclear, as we’re not sure what rhyme or reasons there is to the various creatures that show up to do (we assume) Krampus’ bidding.

Nonetheless, director Michael Dougherty (who made the Halloween-themed “Trick ‘r Treat” several years back) revels in the tension and excitement provided by a supernatural home invasion, and he keeps things moving fast enough that we don’t have much time to ponder the details, or to notice that the dialogue tends to be flat. (“It looks like Martha Stewart threw up in here,” says Aunt Dorothy upon arriving at the festively decorated house, apparently bringing her references straight from 2002.)

The creature effects are convincing and goose-bumpy, but what impresses me most about the film is its commitment to its decidedly un-cheerful premise. Friends, this movie’s content is PG-13, but it has the cold, black soul of an R. It’s appropriate for families with older kids (ages 10 and up, I’d say), though only the most macabre families will take delight in it. Gleefully do I imagine Mom gasping in shock while the teenagers titter and the young children cry in terror. All that without any onscreen bloodshed! I don’t know who this movie is for, but I’m glad it exists.

B (1 hr., 38 min.; PG-13, moderate profanity, violent images, some intense themes and scariness, the presence of an old German woman.)