Altar of Cthulhu

{u}{t}, discard a card: gain control of target creature with converted mana cost{x}, where X is the discarded cards converted mana cost
{b}{t}, sacrifice a creature: put a soul counter
on Altar of Cthulhu. then, if there are 3 or
more soul counters on Altar of Cthulhu, sacrifice it and search your library for an old
one