It seems like Karador, Ghost Chieftain would be a great card to add to the Graveborn deck. What do you think?
{Karador, Ghost Chieftain}
Just a note: if you put curly brackets around the cardnames, it links to the card itself.
As to Karador, I think he would be at home in a similar deck to the Graveborn, but the actual deck can't actually cast the big creatures in the deck. It's monoblack mana base, but reanimates {Blazing Archon}, {Verdant Force} and other off color creatures.