I'm sure someone else could give you a better guide for it, but here's my 2 cents from fighting him a bit and maybe this could help:
Running helps, even if you're a crazy berserker you must know when to fold. His gas grenades can kill you real quick, and he also has normal grenades that can kill you quicker if you're in the wrong place. So it's all about keeping track of where you are, where he is, and never being in the "wrong" place.
When he changes colour and drops smoke grenades, he's looking to drain someone. He won't stop until he heals, and he heals fully, so hurting him before he's done it is wasted time. Let him heal off of someone, as soon as he's done you can hurt him again, but keep in mind the above and to keep moving, keep track of where he throws his grenades.
I'm sure other members can give you more insight but to boil down my experience, keep an eye on where you're standing at all times and whether it's a dangerous place to stand. Don't bother hurting him until he's finished healing, then lay it on thick, but keep moving so he can't lock you down with his grenades.