What's the deal with the Anvil boss?

Not so long ago my two trusted thralls and I beat the Anvil boss, no problem. I got plenty of weapons, three full sets of armor and everything. After the end of the fight both my thralls still had 3/4 of their hp left. Now? the moment we get the boss close to 1/2 of his hp both my thralls show 10% of their hp left.

Same thralls, same weapons, same buffs but way different outcomes. Was the boss buffed or something?

No but he has 3 different weapons he is using and they do different things at each stage. Some of them are easy for thralls some are hard.

I know about the attacks, but we used to take him down without my thralls taking too much damage and now we can’t bring him down to even 50% of his hp. Weird.

Keep an eye on the weapons. My guesses are you are either moving the boss around a lot so that when he does certain aoe spells that they take a lot of damage or that you get caught in the riposte attack with the sword with the riposte skewer and its subsequent aoe spell.
What I did is that I learned the fight solo first with a full 20str/vit/grit build. Then when I was understanding what the boss does I started adding the thrall first in the third phase, then later on in the second and now in the first. But my thrall is a 6100hp 2017 Armor fighter and often ends below 2k health at the end.

I appreciate the tips but funny enough, I never really changed my tactics when fighting him. Strange.

But the fight isn’t the same each time

You guys are lucky; I couldn’t get past the second phase playing solo, even with good armor and a gouging spear. The first phase goes fine, but the second turns into a mess: if you aren’t in the circle of the arena, the boss starts glitching out so badly (on official servers) that every attempt ends with me getting disconnected. I could handle the corruption and poison, but whenever I stepped out of the arena’s central area, the boss wouldn’t know what to do: every two or three hits, it would run to the center to use its AoE attack—even though the player wasn’t there—causing it to lose aggro and regain all its health. I tried tricking it by using the environment for cover, but that hadn’t been factored into the fight’s design. I’ll give it another shot when I’m in the good mood.

I just fought him, dodging the attacks when possible, I did go trough a stack of potions each time but i did find plenty on route. I never stepped out of the circle, there was enough room in the circle that I could get out of melee range to drink a potion. Each phase has an action that he just stands there so you can do a lot of damage during it.
What was your build fighting him? I was full grit, vit and either str or agi. So I got the damage but also the defense. My horse and thrall I parked (stand tehre and defend) just inside the room.

I’m not entirely sure, but in another thread, a player mentioned significant differences in boss AoE damage.
That could be the difference…