The film was originally to release on November 25 but was pushed back to December 4 to coincide with the Krampusnacht, a traditional Austrian festival held on December 5 that celebrates the Krampus coming to punish naughty children.
Michael Dougherty describes the Krampus in this film as Santa Claus's shadow: "He's not the unstoppable monster that kicks down your door and rampages and grabs you. There's something darkly playful about him. He's having a good time doing what he does, and he enjoys the cat-and-mouse aspect of it."
The Krampus's final design was distilled from various postcards and illustrations of the creature over the years.
Krampus is a huge part of Austrian and German folklore. In Austria and southern Germany, they have "Krampus Runs" where grown-up men dress up as Krampuses and parade through the city streets and scare children.
Max's mom alludes to "the noodle incident" that estranged the family from a neighboring one. The noodle incident was often referred to but never explained in the Calvin & Hobbes cartoon strip, and Krampus also leaves it unexplained.
Michael Dougherty described the film as a darker version of a Christmas family film: "Christmas movies exist in their own little snow globe, where a clashing family, no matter how sick of each other, always manages to overcome their differences and live happily ever after. But what if the family's issues escalated, and then they sort of allow Krampus to seep into their reality?"
The opening sequence was shot on location in a single day at a department store in New Zealand.
Composer Douglas Pipes described his music as a "collection of twisted Christmas carols, with pagan thrown in." He incorporated the sounds of chains, bells, bones and animal skin drums into the score, and had choirs chant and whisper in different tongues.
The Christmas photos seen during the ending credits were gleaned from various cast and crew members.
Understandably, with the controversy that surrounded other Christmas horror movies like Silent Night, Deadly Night (1984) and Black Christmas (1974), Krampus (2015) was a hard story to sell. It wasn't until Legendary Pictures agreed to a PG-13 rating that Universal green lit the movie.
Michael Dougherty originally wanted to use the Universal Studios logo from the 1980's at the very start of the film.
Krista Stadler was cast at the last minute as Omi after three previous actresses bowed out from playing the role for various reasons.
In Max's room you can spot toys of Gypsie Danger and Leatherback from another Legendary Pictures film, Pacific Rim (2013). There are also posters from the show Rick and Morty (2013) and Robot Chicken (2005).
Just as the camera pans out from the A Christmas Carol movie on the kitchen television, there are many different Austrian desserts completely filling the counter and middle table, from Vanillekipferl, Linzer cookies and Christmas stollen bread on the counter. This helps establish the family's rich Austrian heritage to shadow what is to come.
In Max's letter to Santa Claus, his full name is Max Engel. The name "Engel" is the German word for "angel". This hints at his family's Austrian heritage.
In the movie, Max shares some candy from his "Halloween Stash" to comfort his cousins. Inside you can see a lollipop identical to the one used as a weapon by the demonic child Sam from Michael Dougherty's movie Trick 'r Treat.
Was dedicated In Loving Memory of director Michael Dougherty's mother Ramona Grace Dougherty.
In a cut scene, the fathers hear a blizzard warning for the Central Ohio area that covers "Franklin County, Delaware County, Ramona Falls, and Warren Valley." While Franklin and Delaware Counties are real (and place the film somewhere in or near the greater Columbus metro), Ramona Falls is really in Oregon, not Ohio. Warren Valley is the fictional town where Michael Dougherty's Trick 'r Treat took place.
Italian theatrical release was originally set for December 3rd 2015, and trailers were even shown in theaters, before being canceled.
At the beginning of the film, the TV in the kitchen is showing a news broadcast with the scroll saying, "Season's Greetings." Season's Greetings was a 1996 animated short film directed by Michael Dougherty that introduced Sam, the demonic Halloween spirit from Dougherty's cult classic Trick 'r Treat (2007).
Max's mother had the Santa family pictures taken, made and framed all that same night at Mucho Mart where Max's store play was on the Friday before Christmas which would have been the following Monday. In the pictures they are all wearing the same clothes they entered their house that night as can be seen when she hangs the newest framed picture on the wall after getting home.
The house Krampus is standing on in one movie poster is a different house seen inside the snowglobe held by Krampus on the other movie poster.
Many of Krampus' minions are also real Christmas/winter folk figures in European cultures, such as the Yule Goat (Scandanavia). The creatures with Icelandic names (Stekkjarstaur, etc.) are named after the Icelandic Yule Lads who are said to visit homes each of the twelve nights before Christmas.