the december event uses Stink bugs, available to get through explore or poops. during this event, up until the 25th you can give or get bundles or poops bundles do not have stink beetles.
What to get
in this even, you want ALL of the apps, or at least all body apps. decor is very irrelivant, as the apps are very sought after in the next year.
the total sum of stink beetles you need to get the apps:
715 for marking apps
640 for mane apps
990 for body/base apps
OR 2345 overall.

for 25 days, you want to get AT LEAST 91 stink beetles a day to be able to afford one of EACH applicator. or induviually for each (rounded)
29 stb marking apps
26 stb mane apps
40 stb base apps

there is a total of 26 apps to get, so be careful to not buy the same one twice if you want them all!!
you also want to be active in chat during this event, as that tends to draw more attention to your den, aka where you get bundles/poops from. you want to try for at least 200 bundles, and remeber to be grateful for everything you get!!