Comments posted to our Dark Souls 3 Wiki
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
If you're truly struggling just spank him in the back with dung pies and make him toxic.
I meet 2 Havel in same place and the same time. Too much chalenge.
At NG+9 he has 3456 health
At NG+10 his health is 3556. Both measurements were done using poison cloud.
At NG+11 his health is 3606 measured again with poison. My preliminary conclusion is that the game changes after NG+7 but the speed of these changes is slow and maybe will be even slower with increasing number of NGs.
Use snap freese on him without been detected it couse agood damage and he will not fight you until you get detected