You guys did it multi, but I tried single. I couldn't make a dent. I ended up having to god mode it. Tried hiding behind pillars. He obliterated them. Tried the run and med up, but he healed faster than I could damage him even when I was actively hitting. So it was a losing game for that. I tried kiting him to my house, and using it as cover while I plinked from the windows with frost arrows. He obliterated my house (stone and tar roof).

I'm about to start another play through, slowly, on a different seed. I might try the lox bomb I saw.