So I went to my inventory, and there is a Mysterious Costume Trunk in it for some reason. Judging by what items it's sitting between, it appeared sometime between me leaving last night and coming back this afternoon. I did not buy it, I didn't get any notification saying that someone sent it to me, and unless there's a random event that I don't know about that gives you one, I have no idea where it came from or what to do about it. Anyone have any ideas on where it came from? Is this a thing I should make a ticket about? (and if so, how?/Is that hard to do?)

It's an achievement prize for having 5k+ wardrobe items :P

it's the prize for having 5,000 items in your wardrobe. Did you get 5,000 items in there?

Oh wow, well I feel silly now ^^; After checking the achievements page, that seems to be what it is! And checking my wardrobe /was/ the first thing I did today, and the last thing I did yesterday, so that makes even more sense, haha. Thank you both! ^_^

Lol I'm glad you got it figured out! :)

no problem :) Congrats on the achievement~