Yay, I got it!
- I had visited the AC every day, collected prizes, and to the best of my knowledge, watched every animation all the way through.
- I changed my shopkeeper from an Island Uni to a Christmas one
- All of my AC items were in my SDB.
- I had two Icy Snowballs in my inventory, although I really don't think that matters since there are people who didn't have any snow items out and still got the sidebar.
- I did NOT have any snow/ice pets or wintery/snow painted petpets.
- I did NOT have a winter-related avatar (for the record, it was the one with Hoban the Navigator in it.) Seeing as how people got it with different avatars, I don't think this is a requirement.
- All of my pets were delighted, and very full except for the Wakster, who was full up. Don't think having your pets in any particular status is a requirement either.
- My Uni played with the Holiday Mystical Tiki Idol, and I know I also played with the Christmas Pirate Krawk Plushie and the Judge Hog Action Figure (older AC prizes) this month. So I don't think playing with your prizes disqualifies you for the sidebar.
- I did NOT sell any of my prizes, donate any of my prizes, put any prizes up for trade, or make any significant contributions to the money tree or the Tombola this months. I did give away some of my prizes, but they were to side accounts for other pets of mine (example, I sent the Snot Cookies or whatever to my spooky-themed account, thinking my Mutant Bruce would like them better than any of the pets on my main.) I didn't give away any prizes to an account that wasn't mine.
- I did NOT play Snow Wars this month.
- I don't think I played any Terror Mountain-related Flash games, either.
- I've been to the Snowager many times this month (it's one of my dailies). But I'm pretty sure I did that last year too, and I didn't get the sidebar then. I've done some Taelia quests, but I only completed a few, the ones that weren't expensive. I honestly don't think either of these are requirements.
- I did NOT have any snow/ice/winter BD items equipped.
It's looking more and more like you had to have visited the AC every day and/or collected the prizes... but I could have sworn I did that last year and I didn't get the sidebar then.