Shot him until he down to the floor, keep shot him and get closer to him until appears the
case sensitive buttons then finish him (repeat this procedure several times!)

Full waklthru from me:

Throw fire glaive at monster a few times, to make him chase you.
When he is chasing you fire him again, and shoot him how much you can before he "smoke".
After he is smoking, fire him again, and repeat it until he is dead.

while the monster is in flame is very vulnerable...keep it in flame and shoot as much as
you can... if it is not in flame or burned, no damage taken..

Once you get him down form the pillars (not perminently down yet)dodge over to the side
and repeat that sequence till hes down perminently. When hes down, keep throwing a power
throw with fire at his head. Once he starts flashing red go over to him and do a finisher
(it wont finish him but it will do massive dammage). soon he will die.