LOS ANGELES—“Flesh for the Inferno,” a cinematic gorefest about a pack of demonic nuns, has little in common with “A Christmas Reunion,” a Yuletide romance about a Madison Avenue executive who inherits a small-town bakery. The one exception is the movies’ writer, Michael Varrati, who specializes in two very different kinds of cult films—horror movies and Christmas movies.
“Tales of terror and tales of tinsel,” he said.
The 34-year-old Hollywood screenwriter’s other credits include “The Sins of Dracula,” “Broadcasting Christmas,” “They Stole the Pope’s Blood!” and “A Christmas in Vermont.”
The work makes him particularly busy during two specific windows—the run-up to Halloween and the Christmas season.
“I’m only popular in October and December,” he said.
Behind the dozens of feel-good holiday movies that spring up on cable each winter is a fraternity of writers, producers, directors and actors who moonlight in skin-crawling scares. Frightening takes on the Christmas season such as “Silent Night, Deadly Night” have become cult classics. The Christmastime schmaltz, nonetheless, comes naturally, they say, since both genres adhere to strict narrative formulas, are produced on slim budgets and carry the support of obsessive fans seeking a cathartic ending—whether that’s salvation or survival.
“They’re flip sides of the same coin,” writer and director Ron Oliversaid of the two genres.
Fans of Mr. Oliver’s recent “My Christmas Dream,” about a department-store manager determined to build a mind-blowing holiday display, may be surprised to learn he got his start in 1987 with “Hello Mary Lou: Prom Night II,” about an undead prom queen who returns to claim her crown.
“There’s a comfort factor with horror and Christmas,” he said. “You know what you’re going to get. It’s kind of like McDonald's.”
Bob Clark, who directed the 1983 classic “A Christmas Story,” about a boy who yearns for a Red Ryder BB gun under the tree, had previously helmed the fan-favorite “Black Christmas,” about a group of sorority sisters terrorized by a serial killer.
When he began working on Christmas movies about a decade ago, Mr. Oliver found writing in ways that would delight audiences wasn’t much different from terrorizing them. To build tension, every scene should “end with a question mark,” he said. “Except the final scene, which ends with a kiss or a murder.”
Audiences of both genres are discerning, said director David DeCoteau, and must be pulled in by the first two minutes.
In his 2016 feature “A Husband for Christmas,” about a graphic designer who finds love at work, he opened with a flash-forward that alludes to a happy relationship. “That really teases the audience.” In another 2016 feature of his, “Sorority Slaughterhouse,” he opened with the suicide of an adulterous university dean, whose blood splatter causes a toy to become a “killer clown doll” that murders coeds. “It’s a taste of what’s to come,” he said.
“A Husband for Christmas” and “Sorority Slaughterhouse” both star Eric Roberts as a design-firm executive and the homicidal college administrator, respectively. “He’s very versatile,” said Mr. DeCoteau.
Production companies are working overtime to keep up with demand. Horror has always filled the catalogs of streaming services and on-demand providers, and the bevy of cable channels airing Christmas movies are posting record ratings this year. Since launching its “Countdown to Christmas” programming on Oct. 28, the Hallmark Channel said it has been the most-watched cable network among women ages 25 to 54.
That’s been a boon to actors such as Nelson Wong, a Vancouver thespian who appeared in seven Christmas movies over the past few years, lightening up a résumé that had featured thrillers and horror gigs.
He recently portrayed a doctor in both genres. In the bloodfest “American Mary,” he played Dr. Black, a medical professional who enjoys practicing macabre experiments on patients. In “Every Christmas Has a Story,” his character, Dr. Kenny Kwan, is an expert in Christmas-tree ornaments who helps a Scrooge-like news anchor find a new appreciation for the holiday.
“I’m usually either the sidekick or the evil minion,” he said.
Both genres are supported by audiences who track each release, whether in Fangoria magazine, a periodical proclaiming to be “the first in fright since 1979,” or on a website called “It’s a Wonderful Movie,” which calls itself “your ticket to Christmas movies on TV!” Fans feel an intense kinship with their preferred genre, establishing rules they don’t like to see broken, say writers who hop between the two.
Horror-movie rules—knowing a character is doomed the minute he says, “I’ll be right back”—were subverted by 1996’s “Scream,” which toyed with audience expectations of the genre. Christmas-movie viewers have little tolerance for such irony, said Mr. Varrati. “Movie Christmas has to be the best version of Christmas.”
Another cardinal rule has emerged. “The channels want snow, snow, snow,” said Sam Irvin, a veteran of both genres.
While directing “I’m Not Ready for Christmas,” about a young girl who asks Santa Claus to make her Scrooge-like aunt tell the truth, Mr. Irvin covered a Salt Lake City set in September with white foam also used at airports to soften a plane’s hard landing. The foam looks the part, but tends to melt after 15 minutes in the heat.
It’s much easier to shoot a grisly horror scene these days because most of the blood is now computer generated. “It’s been very freeing to say, ’We’re going to add the blood later,’” he said.
Soon after finishing another holiday feature, “Christmas Land,” Mr. Irvin directed “The Wrong House,” a Lifetime movie about a family that moves into a new home and finds they’re being stalked by a homicidal maniac.
It premiered the day after Christmas. “Counter-programming,” said Mr. Irvin.