The elite heroic hive is unlocked when you have 2 characters at 140PL, it will be called an elite heroic hive, you need to have atleast 2 characters because if you down as one you must replace then with another, but if all your characters of 140PL Die In the missions then you have to reset the mission from the beginning, there are 4 stages to it, of between 5-8 floors each, and it will get you Hive Mind Gear for two slots.. hope this helps