Black kat, Apocrea, Tortodrones, box rotation, things like cyber monday, casino, and everything else that involves getting things that you can trade really...
I feel this could make the game feel less on hiatus and give to some players a bit of more variety in terms of getting money/trading/getting stuff they want in a more optimal speed that's not just farming Fire Storm Citadel to directly buy that thing you want to get. Don't get me wrong here though, I'm not saying that the events should end sooner, I'm saying that the time between them should be shorter (even though with promotional boxes, both making it be available for a shorter time while decresing the time it takes to get an other one should actually be beneficial for the game's gainings if not mistaken).