So I've been giving it some thought, and I believe I've come up with some of what Yuletide magic can do:
Cold (being essentially Winter)
Slumber (winter being a time of hibernation and rest)
Travel (Santa is known for his ability to visit every house in the world in one night)
Divination/spying (He knows when you've been sleeping/awake. He knows when you've been bad or good... which very creepy when you think about it)
Infiltration (He essentially breaks into peoples houses)
Protection/Threshold (I'm kinda iffy about this one. Christmas is all about family spending time together, sitting in front of a warm hearth, and living in safety. To me, that implies the power of the threshold, but maybe not...
)
Rebirth/Renewal (The celebration of Yule and Winter Solstice was largely about marking the return of the sun and the eventual transition to kinder seasons) (Thanks DFJunkie, for the idea)
Thoughts?