That is a very difficult fight, especially if that is the first time you're doing it. I recall that should be a level 6 fight. I tried doing it on level 5 and was completely obliterated a couple of times on my first run through. So, I have to wait till level 6 before reattempting to make it easier. Having a better understanding of the game also plays a part of making the fight easier, e.g. knowing some good combo to bring armor down real quick, e.g. adrenaline-rage-chameleon-snipe. On my first play through with limited knowledge, what I did is to summon totems and summons to help. Sometimes the mob will prefer to attack them and so they spend some AP on lesser foes
Start on the high ground on the right. He will teleport to you. You have the option to use source power if you have acquired it. If you have not, focus fire it's armor down for CC and teleport the lesser mob down, especially the archer and melee.
It depends on your party composition and build. Since you're having an range build, you can teleport him to the low ground. Use your ranger combo, adrenaline-rage-chameleon-snipe to bring his armor down then CC. The key is to CC him preferably in a turn or 2 before he kills you. It will be easier once you get the big gun on CC or down.
If you still fail to down him, level up to 7. Then he will be cake.
Hope this helps.