Xyros, the Soul Reaper

{x}{b}: Return target creature from your graveyard to the battlefield, where X is the creature's converted Mana cost.
{g}, sacrifice a creature: target creature gets +1/2 X +1/2 X, where X is the sacrificed creature's converted Mana cost
{2}{g}{b}: Choose target creature on the battlefield and target creature in a graveyard. Put target creature from the battlefield into the graveyard and target creature from the graveyard onto the battlefield.