i believe it was removed because of players abusing the sleep status. When you get affected with sleep, you cannot move, but you regain health. Except for overlooked levels, it will probably not come back to the arcade permanently.

After arcade gate customization was taken away, the Starlight Cradle levels were temporarily re-available at depth 2 in the clockworks for about 2-4 days.

The sleep status prevents players from moving, shielding, and basically turns you into a huge target for enemies. You will heal slowly after a certain time, but not too much(Granted, tier 3 sleep might be more potent and thus abusable). When put to sleep, players are put into the "/sleep" animation. However, this animation is pretty twitchy and buggy in of itself.

I remember a Three Rings spokesperson saying something about sleep being something they'll look into in the future, but that might have just been to make us stop talking about how much we wanted a buggy status put back into the game. If the animation is fixed, I would love to have a sleep status to be thrown into all enemy types and have a new status to play with.

Seriously, imagine a sleep-themed shadow lair of the next boss we'll be getting for tier 3. That would make players dread the status and be pretty amazing while doing so.

It was in one of the gates months ago, the status is extremely buggy, when being inflicted by sleep the knight looks as if it's having a seizure.

Three Rings can't think of a reason to actively change something which will not result in a tangible effect on the game.

I was fortunate enough to sneak in a run or two when that Starlight Cradle level accidentally showed up in an Arcade gate, which I figure was maybe my only chance to ever face the legendary Sloom. I can see how the Sleep mechanic could probably use some tweaking, but it was fun to experience it in action, and I'd like to see it return in some form.