I have attempted this quest a couple times. As part of the quest I need to kill a mage type mob that has a permanent "bubble" and I can not do any damage with any spell or CC I have. I Kited one and his imp a little way off to avoid other agro and kept healing myself waiting for his bubble to go away or for his mana to run out. After 20 minutes and no mana used and mob still at 39% (same as when bubble first came up) I gave up and ran off.
What am I missing? How does one kill these to complete this quest?
Thanks