Level 25 Runes on two items, reset attribute points where I put any extra beyond 1k strength into dexterity, improved passive damage by removing unneeded constellations, removed lycanthropy points and put them into the Grim Ward skill until it was max, and I was able to EASILY defeat Baal in a matter of seconds with 100% (was probably 60% before) chance to hit and 15% chance to critical, with my Maul Druid/Barb.
The Grim Ward was my last adjustment. Before that Baal would autoheal to 100% even if I got his health down to 50% very quickly with all the other changes.
MYSTERIOUSLY, Baal didn’t heal at all and died immediately with no explanation. It would be nice if these mechanics were less aggressive and a less powerful character could defeat Baal, especially considering it blocks you from other passives in Act VI. I was level 92.
Nightmare also had autoheal but due to the bosses being less powerful there’s always ways to work around it and kill the bosses including Baal. It’s only really a problem in Hell with some characters. It appears that I hit a DPS threshold that shattered Baal’s ability to autoheal rather than it being an actual skill or trait I had, making it completely not obvious what would kill him.
My Holy Shock build was highly successful but was better able to defeat endgame content assigning more dexterity on him as well, but it wasn’t needed at all to complete Hell since Holy Shock doesn’t need dex, though lightning storm and such did.
EDIT: I now have that SAME problem with King Leoric, but now I’ve already made my build as potent as possible so there’s no escaping the loss of a devotion point. But at least here I can continue to Diablo.
I DID use strategy and got him under 10% health only for him to heal himself to 100%
EDIT 2: Right after editing this post I defeated him. I believe it has to do with damage over time, if it’s high enough the boss doesn’t use his skills like heal. I hit him extra hard and maintained that, he failed to heal in time.