Wyrm of Worlds
The Wyrm of Worlds was an ancient and powerful demon lord from the Netherworld. He was originally summoned to the Prime Material Plane by Darnashta'i, a Tsol'aa who hoped to use the demon's power to protect his forest against the advance of the newly created humans. Pretending to be under Darnashta'i's command, the Wyrm used an evil ritual to slay all of the humans in the forest. Next, however, it used the same magic to slay all of the Tsol'aa. Darnashta'i had never had enough power to actually control this being - it had simply been playing with him. To bring further fear, guilt, and horror to the Tsol'aa, the Wyrm then ripped the forest from its previous location and placed it deep underground, creating a magical portal to provide it with the necessary sunlight, forming the Underground Forest of Azdun.
Before the demon could progress further, however, Gaia manifested and rebuked him for interfering in Her realm, matching wills with him briefly before imprisoning him in a stone deep within the forest of Azdun. As punishment for his sins, Darnashta'i was set as the eternal guard on the bound demon.
The Wyrm was stronger than the Earthmother had thought, however, and during their apparently one-sided battle had managed to strike Her, infecting Her with a seed of his own hatred and arrogance. This seed grew, eventually causing Gaia to slay the elder god Twilight in what became known as Gaia's betrayal.
With Gaia's passing, however, the spell that held the Wyrm weakened. Acting discreetly, he quickly bound terrified Darnashta'i into the stone where he had spent so many centuries, and began to move against the emerging power of Demeter. Lacking a corporeal form of his own, the Wyrm choose to invade the mind of the sleeping Celani who was to become Demeter, much as he had done to Gaia so many years before, but on a larger scale. Over time he solidified his control, planting seeds of arrogance and malevolence within the goddess until the day arrived when he finally grew powerful enough to seize control entirely, overthrowing Her in a fierce battle of wills. Demeter was banished to the Netherworld, and the Wyrm retreated into Azdun to recover from the struggle, diverting energy from Demeter's shrines to himself.
In the year 402 AF, the armies of Matsuhama and Mhaldor moved against the neglected shrines of Demeter, causing the Wyrm to once again awaken. Carefully constructing visions, he urged the remaining members of Demeter's Order to rebuild the shrines, and eventually went so far as to manifest in the form of the goddess himself, alarming the forestal community with his bile and venom. Soon thereafter, Darnashta'i was discovered in his prison, the barrier to which was burned down with the death of the fire spirit Krrathknar, and the remaining shrines of Demeter were decimated to such an extent that the Wyrm was forced to retreat again into the forest.
In the Netherworld Demeter experienced many horrors, changing fundamentally in Her essence. With the destruction of Her shrines, the Wyrm's source of power, which were suspected of causing strange forest fires across Sapience, She was able to overpower Her imprisonment enough to send visions to some forestals. In response to these visions, a ritual was performed to lend Demeter the strength to escape the Netherworld and return to the Prime Material Plane. In the form of a shrouded woman, She immediately challenged the Wyrm. After a brief but dramatic contest, She was able to defeat and bind the demon lord once again, asserting Herself as the reborn goddess Melantha.