A few useful tips when fighting the demon commander:
- Everyone probably knows this but you get some black/green smoke around your character. This is your signal to get the F away. Fade step or similar skills help. Or pop those skills that makes you invulnerable, like fade step or walking fortress.
- You can run out of the range of this skill aswell. If you have the aggro it is good to know when he pops out, has he will once usually pop up somewhere away from you and fire two shots, then fight. Once he goes back down he will come up under a player. Thats your signal to start running. If there is little or no lag, this will always get you out of his uppercut range. Just dont stop running until that black smoke is gone. Skills like stealth (higher run speed) and charging bull can also get you of range. Things like leaping shot can also work but its unreliable. Running is a better option.
- Fight the demon commander inside the room, and whoever who does not have aggro fights or control the adds coming in the doorway. If you try to leave you will most likely get overrun by all the adds like wraiths and fear demons.
- If you have a skill like shield wall, you can stand next to a wall to force the demon commander up in front of you. That way you can block his uppercut and gain guard.
- If you have someone who has barrier and knows how to use it, you should be fine. He should know that barrier is most important right before the uppercut and he should also know who has aggro. If you play keeper, try to notice this. If you manage to negate his uppercut he is almost as easy as the red templar commander.
- Good luck! 