On the eredar twins fight in sunwell, aside from the massive raid damage, there are these little shadow fiends that randomly attack and stun healers and ranged dps. They are untargetable and unkillable, and thus, unavoidable.
HOWEVER
It seems that by using a torch bracket, as well as what seems to be wall climbing (you "stick" as you jump), you can get on a sort of ledge lining the room that shadowfiends cannot access.
http://img100.imageshack.us/img100/9...8002205zm0.jpg
Note the candlestick thing on the left hand side, and the raid on the ledge, safely out of reach of the shadowfiends.
Yes, you can tank the twins in range of the wall.