Sorry to double-post, but I've finally got something.
Strategy:
Forget what I said about using him against Evil opponents. If they somehow acquire the Hammer of Dagda (or the Wheels of Dagda)*, then they can slaugther your Inviolates without consequences. Instead, send him out against Good enemies to fill up his Corruption Meter as early as possible, ending the threat that the weapon poses while gaining a powerful Demon unit.
Pedia (First Draft):
In a place far away from the known nations of Erebus, the Angels of Dagda hid a weapon of great power as a contingency in case the Godswar starts anew. Known as the Hammer of Dagda (or the Wheels of Dagda according to other reports), this weapon was aimed at the servitors of Ceridwen, one of the greatest threats to peace. It had the power to dispel any glamour, and render void any curse triggered by an Archmage's death. Thus, it was regarded as the greatest threat to those who serve the Queen of Pain.
Not merely that, but the Elohim had no foothold in that land, so Dagda's servants founded an order of figthers, who used their own inner strength in conjuction with exotic weapons that were as deadly as they were beautiful. Even in the Age of Ice, this order remained formidable in the unknown lands, using their styles to defend the common people.
However, Ceridwen's reach was vast, and her mind ever-brimming with schemes. As the civilizations in the unknown land rose up again in the Age of Rebirth, she found a way to achive her ends in the best way she knew how, by using the attachments people form in the course of their lives.
One of the progidies of the order was a person named ___________**, whose defining trait was his love for his village, a small hamlet situated in one of the most beautiful valleys in the land. One day, the local ruler charged its inhabitants with false accusations of treason, and ordered them put to the sword, down to the last child. Not merely that, but his most trusted advisor, an Inviolate (strangely enough, the accounts refer to this person as a male) put a curse on the valley to send the souls of those killed directly into Ceridwen's vaults.
When ___________ found out about this, he was furious, and broke into the vault where the Hammer (or the Wheels) was kept, taking it into battle. Against its power, neither the ruler or the Inviolate were safe, and retribution was quick. Then, the Mistress of Pain appeared before ____________, and showed him the manifold torments of Hell, as well as the budding strength of Oblivion. She then revealed that the souls of his fellow villagers have not been subjected to these...yet.
Left with no other choice, ____________, offered his service, as well as the powers of the weapon originally meant to stand against her servants. The goddes then ordered him to set out west, to where her followers have begun the spells that will end the world.
As the figther set out across the trackless wastes, Ceridwen whispered to those of the forces of Good who knew of the Chosen's secrets, revealing that there was a weapon that can destroy her enchantments, but that they would have to slay the hero that bore it; one of her most loyal and fanatical servants. It was her hope that by forcing ___________ to fight the armies and heroes of Good, she can build up the fires of despair and resentment in him, setting him upon the path to Demonhood and negating the threat of the Hammer (or Wheels) forever.
*I decided to have _______ of Dagda as the name of the weapon, as in the Beasitary of Erebus, Dagda's Angels not merely have a feud with the Servants of Ceridwen, but some of them also have the power to undo the strongest spells.
**I can't find a name yet.
