With all the changes like the kill wall and now more invisible walls to stop adds from being thrown the last fight has become more difficult. Now the best way to clear the adds is to knock them on top of the gate where you enter the dracolich fight and run away. The adds will fall on the other side of the gate and be on the bridge where you entered and out of the fight.
I'll also throw in one bonus for CN but I haven't tested if it works recently. It was never widely used so I doubt it was fixed but then again it's not really needed either. For the first spider boss, you can jump into the column behind and to the left of the spider. You jump into the left side and go around to the right til you can see the spider. You are unable to be targeted and can attack freely from here.