It is the dude with the minigun for nightfall. It is super easy, already done with it.
The damage bonus is arc and none of them do arc so that makes it pretty easy for starters. Second of all as you are facing him on the right hand side all the way by where he comes into the room the first time you can hide between the wall and the ramp there behind some boxes. You jump up and shoot him and then hide. When he walks to the other side of the room you have to come out and damage him enough for him to come back to your side. When he comes back to your side you go back to the same method. When he has about 20% life left he will come to the ramp there and can't hit you with anything and just his head right in your sights. Burn him down in about 10 seconds.
Titans go striker for like 30k grenades because of arc. Not sure what other classes have arc.
The fight is easy enough that if you have some arc damage to quickly down adds you can do it straight up without cheesing it. Cheesing it makes it take considerably longer.