spoiler alert!

When you come into the fight dodge the demons incoming attack and kill the two dogs asap. After that go up the stairs and across the little arch way into the corner, 99% of the time he won't be able to hit you and simply fall off the stairs. If you have magic use it on him when he is below. You can also target him and land on him with an attack to do alot of damage. Simply repeat this til he is dead.

The key to killing the dogs is either a fast weapon or a long reaching one, they tend to dodge alot. If you can't seem to kill them, look for an opening run up the stairs and kill them on top, you should have enough time to finish them before the demon comes all the way up, if not fall down the stairs and finish the dogs then bait the demon out to run up the stairs. Practice makes perfect.

I have been able to solo this fight with a sorcerer at lvl 20 wearing full antiquated set. So its possible to do fight without getting hit.