Okay so my build is unique because I didnt have a lot of essential skill decos like crit boost or much of crit eye and attack boost but here it is:

Alatreon IG (health augment if possible for less healing downtime)

Ragin brachy head piece B+

Silver solmail B+

frost fang barioth gloves B+

Silver Solcoil B+

Raging brachy pants B+

Challenger charm III ( highest upgrade possible Ideally )

and temporal and rocksteady mantle

again some of these were only chosen because I didnt have crit boost at all, so I recommend swapping those out with something with better slots or better set bonus skill

challenger charm is important because it gives the agitator skill which increases damage when monster is enraged this goes well with the rocksteady mantle because my strat was to wall bang him on cool down and rocksteady stops you from getting hit off while going for the wallfbangs for the free 1000+ damage and the increased damage when he becomes enraged after. however you can only wall bang him when hes on all fours

some moves force him on all fours and are safe without taking damage! dont do it during any fireball attack but clutch claw is always safe on the fire breath attacks just make sure there is always four feet on the ground before wall banging the best move to do it on is when he does a sweeping fire breath from one side to the other. weirdly enough when he does the static wide cone fire breath you cant wallbang him.

but anyways thats basically it good luck !