Hmm, getting the same problem with Ba'al that I had with Stone's arena fight in that I'm getting one-shotted right at the beginning. Except this time the summon doesn't work because he just does it again once it's been wiped out.
I'm curious what sort of attack this is: I have almost 1,000 HP and (IMHO) very good armour yet I'm being hit with a series of blasts in very quick succession which reduce my health from 100% to zero. Is it really meant to be this difficult? I don't remember it being a problem previously, not even with DKS.