Magma Lord Kaliban is the first boss in Grim Awakening.
He is not hard, but it takes some time to get used to his mechanics. You know what they say, practice makes perfect !
The tank damage is not impressive, the raid damage is minimal and the DPS check can be reached even after failing multiple times as you will witness in the video below
The trick is to get the boulders placed in decent spots so you can use them to LOS.
Making decisions on the spot might also be needed, the chance that a boulder will end up in the wrong spot is almost 100%.
Good luck !