There is paths in between the red circles, sometimes they are really hard to get to, but make use of your dodge if you cant find a safe spot!
just make sure to save one stamina point to use after the red circles, as he does a huge aoe attack that will mess up your world if you don't roll away from it :)
(roll trough the huge blue aoe circle that surrounds the map!)

That last boss is really tough if you havent done it before! it's like being slapped in the face with a brick wall! it's meant to be hard tho!

Thank you for your answer.

I've never seens the paths you mentionned, but I will try to look closely next time!
I'm playing a sorcerer, so at a quite long range. I hope the paths still exist at this distance ^^'

I had massive problems with that battle my first go-round with him as an Electrical mage. I couldn't get to the clear areas between the red circles in time. I was a bit impatient so I decided to approach it with a different style of build as I was already facetanking everything cause of my play-style, so I opted to make a new character that was sword & shield based. I did nothing but nodes I thought would benefit my survivability and viola, I beat him the first time. If you're too squishy and not patient you will just die over and over, I'm sure you can beat him given enough time and item drops, but I opted for a character around my actual play-style.

I know this doesn't really help your current situation, but all I can say is, I did have a little bit more luck as a mage when I would just sit right next to his shield.

I did however learn while playing my facetank guy that you can stun him when he goes into that phase. So when he stops attacking, jumps back into the center and does the shield animation, I would jump and stun him and the animation would go away and viola no more instant death circles from hell. Now it's just a grind till you max out gear and builds!