"The shriveled Old Demon King is now like a clump of burnt ash, but he is the last living witness of the Chaos of Izalith."

Even though there are at least 4 or 5 more demons in the game

I kinda made his teeth longer and sharper cause I liked it more that way.And it you want to avoid any spoilers I suggest you not to read the description any furtherIt might not be the hardest fight, but I really liked it for its atmosphere. And liked it even more after playing DS1. After which I'm pretty sure that Smouldering Lake is The Lost Izalith. Really liked his boss arena, filled with dead demons. And how at some point he just couldn't fight you anymore because he used last bits of his powers in a desperate attempt to take you down. It really gives that "last of a kind" feeling.1 tryOther Dark souls 3 Bosses