Your world has to replicate Santa and his sleigh as best as they can with whatever magic or technology they have access to. What do they do?
The interdimensional Christmas bug is coming to town, and every world needs their own Santa. Doesn't matter if they have no idea what Santa or Christmas is, participation is mandatory and they need to use whatever exist in-universe to replicate Santa's flying sleigh as best as they can.
The following are some guidelines for what a prototypical Santa and sleigh would entail, your world needs to try and replicate as many of these elements as possible.
A fat bearded man or similar species dressed in all red.
A huge sack of toys or whatever the kids in your universe like.
A sleigh or another vehicle modified to resemble the classic shape of a sleigh, one that is capable of flight.
Eight flying reindeer or similar species strapped to the front of the sleigh.
One more flying reindeer or similar species up front with a glowing red nose.
Note that the reindeer don't actually have to be the ones pulling the sleigh through the air, you can choose any propulsion system you want as long as it looks like the reindeer are pulling it.
How does your world pull it off? Who would need to be called in and what kind of equipment acquired to do this? What unique conflicts does Santa face in your world that the "real" Santa wouldn't?
If your world is also conducive to other Christmas characters like Krampus, the Grinch, Frosty, Jesus, etc and you want to replicate them as well, we'd love to hear it!
My science-fantasy world with intelligent animals living in harmony takes place millions of years after humanity mysteriously disappears from the Earth, I imagine how this goes is someone dug up some ancient human artifact that contained information about Christmas and felt determined to do something similar in their present day (wouldn't be the first time, a lot of their science and technology was borrowed from the humans when their ancestors dug up human ruins and deciphered human language). They might pull off a Santa and sleigh in the following ways:
Well all the humans are extinct from the planet and they haven't built Anthropocene Park yet, so best they can do is dress an overweight bonobo or other ape in red and strap a fake beard onto him. Or, if we're using animals that I actually have developed characters for and possibly the much cuter option, Santa Cat!
A sack of toys wouldn't be hard to come by, though they would likely have to be species specific since different animals like different things. Not a huge problem all things considered.
They have something called a Gravitational Slipstream Hovercraft which are nearly ubiquitous as the primary form of public transportation, think of them like aerial buses. GSS hovercrafts are probably by far the safest way to do this, as they can levitate and fly very fast under their own power, have active stabilization to keep itself steady as a sleigh needs an open top, have automatic collision warning and avoidance systems for both flying animals and other hovercraft, and can lift enough weight to carry a massive bag of toys. They would need to rent a hovercraft from one of the airlines/public transit providers, probably the Feline Ministry of Transportation as the Felines are more or less considered to have the best hovercraft tech. Unless Santa has a pilot certificate and is type rated on that hovercraft though, they would probably also need to "rent" a pilot too. From there, they can build a structure that resembles a sleigh around the hovercraft, which luckily wouldn't be hard to do since GSS hovercrafts don't have wings that need to be kept aerodynamically clear, nor do they have rotors or spinning engines that create airflow. GSS engines can still do their gravitational field manipulation from behind the sleigh facade.
They have actual reindeer, who are also sapient just like every other animal, and you could presumably just hire nine of them to pretend to run in front of your hovercraft. As for how they might levitate with the hovercraft while not having anything supporting their hooves, they can use a similar form of technology as a gravitational slipstream drive, albeit several stages more advanced and way more restricted by the government. A quantum interface can levitate pretty much anything within its area of effect. This would probably be the hardest part simply because they need to make a good case to the regulators why they should be allowed to use quantum interfaces in this way, and they would also need a government researcher to ride along with them and to be the actual one operating the quantum interface, possibly even my main character!
Rudolph is pretty easy, just strap a red light to her muzzle and pretend to bully her for a bit! The hovercraft has navigation instruments and would be flying in IFR so she doesn't actually need to shine through the fog.
Realistically, instead of delivering presents to individual houses, they would probably just parade around going from city to city and handing out free swag to kits/cubs/etc along the way. I doubt the government security agencies would give them access to their naughty lists so they'll just have to take their word for it on if they were naughty or nice. This world might have its share of Grinches too, mostly in the form of air traffic controllers freaking out and not allowing them to enter their airspace because their aircraft is "unsafe", such Christmas haters amirite?
In my fursona's world, Santa's a polar bear and the elves are, paradoxically, emperor penguins.
In actuality, that world's equivalent of the Coca-Cola company had more influence on the modern concept of Santa Claus. Or really Santa Claws as he's called. Like IRL, in my fursona's world Santa is a traditional legend.
However, to make Santa work...
You'd need a fat polar bear (easy to find, bears tend to be on the chonky side in my fursona's world) dressed in a red suit. Or green, the whole red suit design was Coca-Cola's idea, originally the jolly old elf wore green.
The sack is a bag of holding. In my fursona's world, magic is surprisingly common, just not relied on due to its fickle and unreliable nature.
The sleigh... I guess you could put a wing enchantment on one.
Toon or toonified reindeer that ignore gravity during the flight. Could also help resolve the whole "white tailed deer" situation with depictions of reindeer if they're basically a mix of the two in traits.
By coincidence, I've had a "Santa AU" story idea for awhile just like this. Maybe material for a Blender short one day if I git gud at animation, who knows.
Furry/Anthro universe, set in near(?)-future. Giant high-tech factory at North Pole makes tons of toys. Huge antigrav spaceships deliver the toys, piloted by "Santa's" reindeer (All 9: Dasher, Dancer, Rudolph, etc.), split into teams to handle each continent. Dunno if any other workers, or if all automated toy-making. Oldass oil painting of the Saint Nicolas (also a reindeer) hanging on the factory wall; operation inspired by his legendary generosity, continued by generations of admiring reindeer (and other Furry species) throughout the centuries after his death.
Squash in as many holiday tropes and not-so-subtle references as possible -- e.g. The Guardians; Dancer makes small-talk about Rudolph and his girlfriend Clarice; maybe squeeze in Vader-San's Synth species cuz this a techno AU and me shameless simp; etc.