one out of all the mobs in the room is the key, you kill that specific one.. and there is no way to know which one it is, but trial and error till you get it and they will stop respawning..
it's all on luck vs time. I've gone into such a kama and had to sit there for 30 minutes before the correct bugger was finally killed and the room was finally cleared....
The easiest i find and safest way is to get a dagger with the stealth and lure, lure a different mob to the front where the port in locaiton is MAKING sure that the mob is at the port in collum BEFORE attacking it, kill and repeat.
This is how we try and do the 78 and 81 kama, there are only a few players that can take on the entire mass of mobs and come out in one peice, usually requires a group of AOE specialized players.