During the fight after we come back from the fire portal, the fire mages appear really too quickly, hardly one is dead than another is often followed by a second a few seconds later and their damage are too strong.
Knowing that the boss will summon other add + colossi and that this is followed by the circle which gradually tightens on us, we often end up with 3 fire mage to interrupt 2 colossus inside the circle,really hard for finish in life this phase.
it's really complicated when you come out of the fire portal.