I'm a fan of the whole "walking corpse" theory. If he's wandering out to devour pokemon and people, I think he's doing it to replenish energy, and if he froze himself internally, it's definitely possible he's dead. Obviously I'd want to know why he isn't part ghost, but the dragon typing is really necessary to tie him in with Reshiram and Zekrom, if everything else wasn't enough.
On a more science-y note, Freezing things is and awesome way to preserve them. (You know, like... in a freezer :bidoof: )
What if when Reshiram and Zekrom exploded out of The ONE Dragon,The remaining pokemon was left so weakened, it used it's little remaining energy to freeze itself in a solid chunk of ice (which is what meteors are usually made of) and when it fell to earth, creating the chasm, the chunk of ice shattering, damaging its body so it was unable to fly. It devoured nearby pokemon, who eventually learned to hide from it (explaining why the Chasm isn't empty) and gained enough strength to wander out and begin feeding on the nearby village. If it was an animated corpse, it would explain the need to keep itself frozen. Cryogenics.
I'd really like to see another form, possible one with an ability or item to ignore charging.
