You want to be careful when you open first door once you are in they base , you can aggro like 10 of them at once which is unbeatable fight ( There is this free drone woman with Crossbow and she can stun you before you could act and then all of them comes and keeps you cc'ed ) , but i managed after few retries to pull them in groups of 3-4 back into the starting room and shoot them with burst fires while they are in a doorway , You can wait a bit before starting the fight so gas spreads and some of them become mutants and start fighting each other this makes it easier , When you transition from the free drones HQ to the corridor you might as well just get killed before you can do anything , so reload until you are first to act . I used Night Vision it helps a lot to see where gas is exactly , also Flashbangs to end the combat so you can bandage yourself and reset all the effects on you , EMP grenades are very good here because you can have like 3 guys with energy shields bunched up - 1 EMP grenade and they are done , green bullets will work well in this encounter as all of them has some kind of Armor , if you got quick tinkering you can put bear trap by the door in the room you start and pull as many as you want and they wont be able to pass it while the first guy is trapped , also you cant let Psionic to cast Doppelganger on you unless you got very much of Electrical DT so best is to flashbang/stun him before you end your turn , Adrenaline Shot for 2 turns and flashbang + run for reset on 3rd turn is good tactic you can end combat heal yourself wait out fatigue and engage them again . If your character has some defensive feats like the one that changes stunned to dazed( which i did not lol ) it might be able to run trough without getting cc'ed , i didnt had it and i was getting Stuned > Frozen > Stuned > Incapacitated till i die , so i had to divide and qonquer . Well now that i know how the fight is i would : Take my Stealth gear ( even if i got 0 base stealth i had some pretty neat stealth stuff crafted ) and just sneak trough it ^^
This was hardest fight in whole game imo , more like this please , also De Pacino guy for Protectorate quest was kinda tough too but not as tough as free drones