(Arcade) Are all of the avatar items randomly unlocked?

I just got my Banapass after playing on guest mode for a little while. When I logged on to Donder Hiroba and saw they had a list of costumes to unlock, all of them (save for collabs and such) were linked to this seasonal campaign(?) on the site. I got 2 of them while I was playing last night, but I was wondering if cosmetics are 100% randomly unlocked? And/or limited time only?