Bosses and some mobs resists

I see very bad new for casters, some bosses have very big resists(and mobs)
That is my pic:

My hero make 0 dmg to this boss, how to kill him? Only melee and ranged ?
Thank u for looking.

one more thing,no resist from mobs at all,i mean i am 200 or 70 lc doesnt meter but lv 1 or .... mobs can see me from far away,like in normal dungeon i just enter and all mobs on me,fix that and u save some lag in game