Phase one: Try to time your ability usage so you can stop enemy child on using his.
Phase Two: use everything you can on the archers, they are deadly here, if your Death Knight is below 50% of the hp at the end of this stage, best to reset then.
Phase Three: 1:26 Night Raven uses his AOE, Counter with Death Knight, 1:08 Night Raven uses ability, Counter with rose knight