I just defeated Moder in less than 5 minutes with a pack of tamed dogs. Moder attacked them (since they were attacking him) while I stood at a distance and shot poison, fire, and obsidian arrows. He never attacked me. Easiest Boss win of all. Thanks to tamed wolves. I prepared for the battle by creating a flat area around the altar, removing trees and rocks, and cutting a path through the mountains to make it easier for the wolves and I to approach the altar. But the actual battle was easy.
While wolves to not attack other wolves or Fenrings, they do attack greydwarfs of all sorts. I'm about to find out if they'll help me against enemies in the prairie.