The Varterral is at the end of the Dragonbone Wastes. If you’re concerned because of how difficult the Harvester was on Hard, don’t worry. This thing is much, much easier. Again, switch the difficulty to Hard or Nightmare right before you get to the boss fight (it’ll be right after an autosave point before a huge clearing). Have Finn set to heal everyone in your party. You, Dog, and Ariane hammer away at the Varterral. When the Varterral summons Dragons (which will happen two times), have Ariane go after them. Keep hammering away with Dog. The Varterrel is more annoying in some ways than the Harvester because it heals itself and jumps around a lot. Other than that, it’s a cakewalk.