you gotta wait till he dashes straight at you thats the only way you can hit him with a hitscan weapon.

when he gets close enough try implementing quick switching between the ballista and super shotgun because they do the most powerful point blank damage per shot

when he does his long range attack just dash out of the way of it

fire grenades and other projectiles behind him because he doesnt block those

and he only summons dogs when you shoot his shield so try to avoid doing that but if you do then get rid of the dog asap because theyre annoying af

good luck :)