Vulgrim

Whenever an opponent's creature dies, put a soul counter on Vulgrim.
Sacrifice an artifact: Put X soul counters on Vulgrim, where X is the sacrificed artifact's converted mana cost.
Remove X soul counters from Vulgrim: Return target artifact in any graveyard with converted mana cost X to the battlefield under your control.
"Feed my hunger and I will feed your curiosity."