How to defeat the gluttony demon
I brute forced it myself. I just made sure I was at max strength going in, especially in celestian power (meditated at the hot spring). During combat I used the celestian time-stop power as often as I could, the invisibility potion, and the magic and HP regen potions (hint, don't wait until you get too low, as they aren't instantaneous). It wasn't all that hard, really.