Metal Warchief

Affinity for artifacts
When Metal Warchief enters the battlefield, for
each artifact that was used to help pay its casting
cost, exile an artifact from target player's
graveyard. As long as Metal Warchief remains
in play, you may cast artifacts exiled in this way.
When you do, target card gains "Affinity for
artifacts" and you may pay {x}, where X is the
target card's converted mana cost.