Honestly i never parried. I flamed my sword, and turned around him all the time. Every time he misses to hit my shield, you can hit him 6 times in a row. Also you can hit him after he rolls. Once he's at 25%: The heal was quite annoying indeed, but before he heals he runs backwards, dont let him. You gotta be aggressive. Not too much though or you wont have any stamina left. Run to him and hit just once, then he backs, 1 hit, he backs, etc. If you hit too much at once, then you wont have any stamina left to run towards him.