My advice is get someone to help you :) I am a storm wizard and a death wizard helped me. I was able to hit through the shields and kill the pox's. Once those are dead, the battle is pretty much over :)
I usually ignore the Pox and go after Mavra first. Mavra's the only one that attacks. Once she's gone you can take your time healing and whittling away the Pox without worrying about getting killed.
It can be a long fight (pack a Reshuffle or two) but once Mavra's dead you've won; it's just a matter of time from there.
