Would a sort of rogue-agent dragon have a place in this? Sometimes an ally, sometimes an enemy- perhaps he broke the morals and was banished, but has power that is still useful enough at times to merit dealing with him?

I'm thinking of a large Black dragon that dabbled in extraplanar magics and corrupted himself slightly with it, rendering him as a creature that doesn't truly belong in this world or any other anymore. His magic might at first seem like normal draconic water magic, but he's done dark things to it that both limit what it can do in some regards but expand it in others.