Zodiark, Ruler of Darkness

Pactbound (When you cast this spell, you may exile
a Pactholder creature you control. If you do, reduce
this card's mana cost by {x}, where {x} is the exiled
creature's converted mana cost. When this creature
dies, return the exiled creature to play.)
Flying, Menace
—
"I am Zodiark, the Shadowwyrm. I am he who
waltzes in the black... I am darkness incarnate... I
will be your shadow, ever vigilant and protective!"