Boss instances

Latales has this feature.

*Latale



And yeah, lots of MMOs have instances. However, Latale's instances are still based in thier own invisible "channels" of sorts, so when too many people are in the instances, people cant enter and start up a new one, which is well and good for LaTale (unless you're farming the Hyunmu set, then it sucks). Anyway, back on topic, as I said many MMOs have some form of instancing, and while channels are probably our closest thing, a game like Latale has both channels and instances, I dont see why Nexon couldnt pull it off too.