I managed to defeat it, no worries. I tell you trick, kill the field guard first and heal yourself when you need it. So save pip points!! Then you can easily kill Foulgaze, you still need high level cards that are good against death and storm. I learned this from dying a lot. I managed also to kill Lord Nightshade in the Stormdrain tower, but it is because I helped another wizard, who returned the favour.
So give and you shall receive. Helping each other is good.