Braand?

"That is the last thing Kegan Rodhe remembers, for now his body belongs to Brand. It is a creature of olden times, perhaps even a casualty of the Rune Wars. It is known in ancient texts as the Burning Vengeance. It is a creature of pure fiery hate that exists for no other reason than to lay waste the world of men and yordles. No one is quite sure how Brand found his way to Valoran, but he began his predations at once."

Sure sounds like a Darkin to me.

Not saying he should be but he would make a decent mid/mage darkin.

Personally they should just make a new one but if they had to reuse an older champ, Braand would def fit.