Cloud Cuckoolander: Raziel, Molly, and to an extent Gabe, who's more than a little disconnected from the normal world. Molly's Cuckoolander status is what prompts Raziel to seek her out, since angels, in his words, are attracted to lunatics because they can reveal their true nature without creating a breach of faith—nobody would believe a crazy person saying they'd met an angel. Fortunately for him, Molly had already figured out she couldn't kill him, or she probably would have tried. Again.
Covers Always Omit A Lot: The part where Raziel raises the dead who attack the church is not really the focus of the book. That doesn't happen until the end. The book is really about following Theo Crowe as he investigates the disappeared Santa while dealing with his marriage troubles. But you would not guess that from all the book's promotional material.
Deus ex Machina: Via Reset Button. At the end Josh explains in better detail to Raziel that what he wants for Christmas is for everything to go back to the way it was before he saw Santa killed.
When Tucker is bitten by a zombie, Josh points out that anyone bitten by a zombie turns into one, so they need to cut Tucker's head off before he becomes one. Fortunately it never gets that far.
Gift of the Magi Plot: An odd variation. At the start of Molly and Theo's relationship, she finally agreed to stay on her antipsychotic medication, which among other things prevents delusions of being an After the EndAction Girl, and in return he finally gave up his pot habit. But when Christmas comes Theo wants to get her a priceless antique sword that would be absolutely perfect for her Action Girl persona. To afford it, he starts growing pot again to sell it, and falls off the wagon. Meanwhile, she's getting him a massive, elaborate bong. To afford that, she stops taking her meds.
Hearing Voices: Molly is a schizophrenic actress who hears a voice she has dubbed "The Narrator" (it's not said if it is the same narrator as the book). Unusual for this trope, the voice helps her more often than it gets her in trouble. She can also hear the dead telepathically talking to one another in their graves; when one of them refers to her as a nutcase, she yells, "I am not!"
Jerkass: Dale Pearson is described as an "Evil Real Estate Developer," and introduced swinging a bag of ice at a salvation army collector(who happens to be his ex wife.) He's also the afformentioned zombie Santa.
Lampshading: A character remarks that the Red Shirts on Star Trek always get killed... and of course, the guy with the red Starfleet command shirt gets offed at the first opportunity.
Let's Get Dangerous: When Theo starts barricading the church doors and windows from the zombies while stoned.
Intoxication Ensues: Mavis's 'special' fruitcake. In her opinion a fruitcake should have just as much flour and dough as is required to make the pharmaceuticals stick together. Ingredients may include Vicoden, Ecstasy, rum, and whatever other narcotics she might have on hand. Theo tries to ban it because the previous year it had put six people into detox, but that's hardly going to stop Mavis.
Red Shirt: Literally invoked. One character decides to wear a Starfleet command shirt because it's a festive, Christmas-y red colour. Another character even comments on how the Red Shirts always died in that series. Guess who gets shot in the head when the zombies walk through the door? Here's a hint. He's wearing a red shirt, and it ain't the guy in the Santa suit.
Saving Christmas: A deconstruction of the Santa's Sick plot, taken to absurd degrees.
Scars Are Forever: Averted. Molly's scar, which ended her movie career, is removed by Raziel as a kind of Christmas present. This actually moves her to tears, but the Narrator naturally breaks the moment:
Narrator: You complete shit bag of sentimental saccharine.
Shaped Like Itself: The first line begins: "Christmas crept into Pine Cove like a creeping Christmas thing..."
Dale Pearson's statement that his Ex-wife is "A nutcase" is said as if he were declaring water is wet.
Talking Animal: Roberto the fruit bat, though the only other person he talks to besides Tucker is Molly, because nobody would believe Molly if she mentioned a talking fruit bat.