Caedus said:
I'm playing a SL 27 thief and he owns me everytime.
Heya.
Characters in DS become far more powerful based on equipment than based on SL. On your second run, you'll probably find that you only increase your SL in order to meet the demands of your desired gear, or for a *slight* increase in stamina and HP. I've got a PvE pyromancer that does about 1,100 damage per hit with a +5 lightning Zwei and Power Within. I'm on NG+ and I'm Slevel 18. Some people have gone to NG++ at Slevel 7, and perhaps even lower.
My advice for this fight is to grab a +5 weapon and +3 your armour. Go to the merchant in the tunnel before the depths and pick up a modifier as well, to increase the damage of your weapon further.
When the fight starts, run forward and a little to the right. It'll probably do a leaping swing. Wait until it's begun tracking your movements while swinging before you roll. Too soon and he'll hit you.
If you get past him, you've basically won. Sprint up the stairs and get on the arch over the door to your right. The dogs will be able to follow you. Kill them. When the demon swings he should fall off the stairs into the space beneath the ledge. Do a plunge attack, rinse and repeat. Good luck!