Sleeper temple hard difficulty

WTF am i supposed to do against the lightning orc? Can´t stun him, can´t parry him, summons a demon in the later half, has like 2500 heath.

As for me, i get killed after 3 hits, can´t retreat if i get hit since he starts to spam lightning orbs. If i get hit by one he chain stuns me into the deathscreen.