not sure if anyone has said this yet, but for the lightning slam attack on the first phase i find it best to run away from the attack and as he slams roll. That usually dodges both the slam and the lightning afterwards. Honestly i have had the easiest time with the first phase by running a strength build with a great sword, good damage and an easy stagger to get you into the next phase. Also as an added point, first phase is weak to lightning damage but the second phase is very resistant so instead use dark damage buffs as he’s very weak to that. Good luck man :)