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r1 spam from light weapons stun locks him. Which is hilarious considering he's Havel. Just don't mess up the timing because his hyperarmor frames are incredibly long. Gotta get the jump on him before he starts up his attacks.
He seems to have somewhat unique AI in that he has phases, like a boss. At about 60-70% health, he will use his shield's skill, then two-hand his tooth. After this, he will never, ever one hand it, although he will, amusingly, try to block with the tooth, generally getting guard broken after only a couple of hits. His lightning absorption will also drop dramatically when he uses his shield's skill (great time to use miracles or other lightning projectiles), but it will return to normal when the skill ends. Also, if you interrupt his use of the skill, he will immediately try again, and again, and again, until he succeeds, which can be exploited.
He's VERY WEAK to frost. Can be kiled very quickly using Snap Freeze and any fire weapon.
If you get a weapon big enough to stagger him you can repeated knock him off the ladder.
I just use a UGS with thrusting charged heavy and stunlock him against the dragon. I took literally zero damage.
In NG++ he has around 3000 HP