I've completed all 8 Elite dungeons, and have Blue QL 10 Talismans in every slot! Obviously, the next step is Nightmare modes! But in order to run those, I have to first defeat The Gatekeeper. I'm primarily set up as a Tank (Blade/Chaos if it's important).
How do I defeat this mode? I've figured out that I need to keep him faced away from the green dude that's going to kill him for me, but he seems to periodically one shot me and I just can't avoid it. What am I missing? Are there further phases or mechanics to the fight?