Energy and death protection are very important here. Make sure you have on the appropriate EQ since the boss has a mean Energy UE that can do 4k-6k damage. Mages should stay on mana shield incase the boss UEs.
I haven't had any issues with the boss changing targets other than when it teleports which is something you'll have to be careful with.
Most importantly, you can stand behind the barricades in the room which will block the bosses attacks. In the image below, you can see the root effect as the white haze and how the barricades don't have the effect in the sqm behind it. The boss is to the SW of me in the image below.
I hope this helps!