Carrion Dragon has the following benefits:
Counts as a Manakin for purposes of Carrion Wood theme (is affected by the Carrion Woods Unholy special spells, notably, Mend the Dead and Regrowth)
Has a huge amount of hp. It's not uncommon to see him breaking the 400+ barrier in dragon form in positivie dominion.
Has a crazy amount of attacks with Sleep Vines and etc.
Has Recuperation.
Base form has stealth, so you can stealth into an initial province, your dominion is raised by being a pretender, and attack a province. This is how CW expands early for me.
His negatives:
Counts as a magical creature.
Counts as undead.
Can't fly (Obvious I know, but the first time I used him I changed form to fly somewhere and forgot he was a dead dragon
I like him with Astral/Earth.