I cant beat it either. However, I have found a way to weaken him (shadowfist commander) fast. You know those flame thrower containers that should have made it hard before you started fighting? You can REACTIVATE THEM! Took me about 2 minutes to perfect, but I finallty found that if you lure him through the fire, he burns like paper! You must put on your shield however. So if you figured this out already help me, if not, hope this helped you.