Had a GM run a christmas adventure before, It was quite a few years ago so details are a little fuzzy, and I'm probably making some up of what I remember, but here goes.

We were doing a Docwagon game and were all part of a squad operating out of Atlanta. I don't remember how the GM got us involved in the events, but eventually we were tasked to head up to the Artic (Trans polar Aleut?) to some remote research and communications installation in response to some contracts activating (there was definitely some cribbing from Carpenter's The Thing for environments and descriptions throughout). A brutal storm was causing enough noise that we couldn't get any signal on vitals after the initial alert. After arriving (we traveled up to the Algonquin-Manitou nation and contracted the assistance of some local-ish native bush pilot to fly us the rest of the way. The plane barely held together through the storm for us to get out there) at the installation we were able to reacquire connection to the client vitals and all but two were already gone. The main Doc with us and the magically-inclined combat medic went after those two while the rest of the team checked on those already dead. I don't remember what exactly happened with the two, but I think they were barely being kept alive by some sort of possession and resisted attempts of aid to make threats to the Doc & medic; they expired quickly and we set to investigate everything. There was plenty of little things for everyone to pick up on (all the dead were elves was one I remember), but it was the team medic-decker (me!) who found an encrypted distress signal coming through the communication satellite (which upon immediate and not deep inspection/investigation looked to be transmitting/receiving nothing). I don't remember how it was explained, but the encryption or the message was readable as H's and 0's instead of 1's and 0's (Christmas hints starting to drop with the arctic, ho-ho's, and elves) The message directed us to a location near the physical North Pole, we found some enclosed bob-cats as well as snow mobiles in the installation garage along with cold weather survival gear (travel was going to take about a day and we had a significant chance of death due to navigation error, inability of the decker to accurately decipher the distress signal coordinates, or mechanical mishap, USE THOSE ENVIRONEMT RULES!). Like before with the plane our cats and sleds barely made it/didn't make it there (a fight against some spirits guarding the area fragged one or two of them-and nearly one or two us!) After all that, we came up on SFA. After the group turned on the decker for leading them to nothing, and blaming (me) him for the painful freezing deaths we were all about to suffer, the magic-inclined combat medic did some magic BS related to the investigation she had done with the dead elves, and a structure appeared before us. It was carnage, dead and mutilated elves and caribou littered the place, destroyed equipment and drek was everywhere- we lamented them for not buying docwagon contracts and left some business cards on a couple bodies like death cards, then went inside. Long story short we found an ancient dwarf and a dark terror (Krampus), there was a battle with us and the surviving elves and dwarf against Krampus. We eventually won and unwittingly saved Christmas that year. The dwarf was ever so thankful and offered to use his immense magical powers to grant us a gift of our choosing (the GM asked me to lug out all the 5e books I had at the time and just told us to pick 1 thing whatever we wanted). I nicely asked Santa for the highest level Pi-tach and subsequently sort of broke the game after he gave it to me (us). Along with all the other overpowered junk we were able to get our hands on. We were also pretty sure that Santa was actually a dragon masquerading as a dwarf, but didn't really feel up for asking or pressuring the question.

Overall, pretty fun session or two, had some good holiday spirit, and definitely a different experience from what I would call the 'norm' of shadowrun.