Arthion, the Dark Master

Flying, trample, haste, deathtouch, haste.
This spell can't be countered. Whenever Arthion is sent to the graveyard or to exile, pay it's mana cost minus X, where X is the number of Shadow Priests you control.
{u}{b}: Create a 0/3 Shadow Priest token.
Sacrifice a creature: Arthion gains +X/+X, where X is the sacrificed creature power and toughness. It also gains all the abilities that creature had.