How do I defeat the Gatekeeper as a Damage Dealer? (The 'Furia' option?)

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 DPS (AR/Elemental if it's important).

How do I defeat this mode? I've gotten him into the 'second phase,' where he floats up into the air after dying a few times to his 'Too Slow' attack, but then he just one shots me after a few seconds. What am I missing here?

I've passed the Gatekeeper as a healer long time ago, I remember DD have a lot of trouble in finishing his test. If you already know the tactics and different steps you'll go through, there is not a lot of things I can tell that would help. But here's the solution a lot of members of my Cabal used:

• You have to create a fresh new skills build (passive + active) to pass the test. A build which would be designed only for the gatekeepers.
• Also our members sometimes even needed to pick new skills in trees they had no interest in, just to be able to finish the test.

So my advice to you and other who might have the same problem in the futur is to create a fresh build dedicated to beat the gatekeeper.