Is this by any chance the one on his right hand? Mine bugged out and was still rendered even with a missing arm (only found out with magick bow aim).

Second time, I shortly destroyed all when he got to shore but it seems take an extra minute to take effect. Still got the achievement. I used the explosive aiming arrow (Magick Archer).

I've done multiple attempts and it doesn't seem to matter which one is left last. Hand, leg, back of the foot, all immune once it's the only one left. And yea I haven't unlocked the magic archer class yet somehow, I tried going back and unlocking warfarer to take him down but I ended up triggering the boss fight anyway when I went down that way so I had to reload Inn Save all over.

I love this game but man is it frustrating in dumb ways.

Try the unmaking arrow for that achievement, personally havent done it but I think it works?

Yea I've heard that's one way to do it. But regardless, whether I'm going for the achievement or not he's invincible, is this bugged?

I used the unmaking arrow and hit him before the bridge. I had to wait till he walked a bit on land before the achievement triggered.

It can definitely bug out. I got the achievement first time on my first playthrough, but on my second playthrough the rod in his left knee is immortal. I don't know what triggers this.

can I ask how you did it the first time? Like which class you used and what your strategy was. Maybe if you remember where he was when he died too?

I think there's a deadzone somewhere in between the ocean and the Camp that he becomes immortal.

Super frustrating, I haven't progressed in days because of this.