Originally Posted by Dragotech
Perhaps you can haz special quests that unlock unconventional Pokemon at the end that would be unusual for that specific region.
You maybe can put a certain Pokemon up for capture.
Maybe a special christmas themed recolor that can be captured.
You could just have a list of gifts [points, eggs, items, and other fun things] and give them out via number generator.
or you could go with KB's idea... though I am unsure of how Team Rocket would be disguised as Santa in all the threads... but you could probably think of something
If the Anime is anything to go by, they use Delibird (which looks like Santa) for communication and delivery at times. That could be the solution.
There could also be a 'double points for posting' or 'all Pokemon half-off and a mad capture spree' thing going. Or maybe something a little more practical, like an item that evolves a Pokemon instantly and free-of-charge (or for a GREATLY reduced charge)? Perhaps multiple of the mentioned at once? Not out of the question to have more than one of those things going on, eh?