I've cleared every single area in Edron before the void entrance. Yet, I could find only 9 bosses, which are Bloodback(Grimvale), Daniel Paladino(Edron Path), Demodras(Dragon Lair), Earth Overlord(Earth Hole), Mad Mage(Lab), Mahrdis(Tomb), Necropharus(i'm not sure but i think it's from Old Fortress), Sir Valorcrest(Crypt), The Old Whopper(Cyclopolis). My best guess is last boss is from Treasure Room at the end of the Cyclopolis path, but so far, I've found nothing. Can you confirm or help with the last boss location? I've been grinding to find those bosses for a few days :D