| Spoiler warning!|
Beyond this point are spoilers! Read at your own risk.
He appears to be a Shadow Dragon, native to the Shadowplane.
Nightwing had two stages, Ground and Flight forms. Nothing beyond that was really determined, though he would most likely employ moves utilizing his claws, teeth, tail, and fire breath, while occasionally gliding to another section of the map during the land phase, while most likely charging the player with his horns or breathing fire in his air phase.
Nightwing would have been encountered during the final visit to Cale's capital, located on a high mesa.