Nidhogg
Nidhogg is a Protogenoi Dragon turned Oneirian god. Reveling in chaos and destruction, it is said that he terrorized the prehistoric creatures that used to live in Swen long before the Shattering. He would use his variety of elemental breaths to tear the landscape asunder.
History
When Vaskus murdered the moon goddess Isha, a fragment of her body fell to Erudite, completely destroying the continent of Swen. Nidhogg was the only being to have survived the destruction, and upon discovering that it was at the hand of a powerful god of destruction, he could not help but admire his work. Thus, when the other gods waged war against Vaskus, Nidhogg took Vaskus' side as he soon learned of the other continents around the world that could be destroyed in his name.
Eventually, Nidhogg was killed during the war among the Old Pantheon, and his body was left in the ocean off the coast of Swen. Eons later when the continent was rediscovered, the Great Spirit had planted the last seed of the Tree of Dreams, hoping to rejuvenate the land. While he was successful, the Great Spirit had accidentally created the Antithesis - a manifestation of the memories of Vaskus that the Great Spirit had absorbed. In doing so, dark magic had stirred within the Tree of Dreams' roots which resulted in Nidhogg reincarnating as a massive dark spirit.
Although Nidhogg remains contained within the Tree of Dreams' Realm of Darkness, on multiple occasions, he has attempted to escape, using his power to control other dark spirits to his aid. During the First Rupture, he was directly summoned by the Goar to attack Zula settlements.
During the Second Rupture, he returned once more to attack the dwarves living in the Kalta Mountains. Though he was only at a fraction of his original power at this point, he was still a formidable foe. Eventually, Maria Martines managed to destroy Nidhogg for good during her quest to stop Antithesis from destroying the world.