Phyrex, Machine's Origin

Whenever an Artifact you control enters the
Graveyard from the Battlefield put a Scrap
counter on Phyrex.
{t}, remove {x} Scrap counters on Phyrex and
search your graveyard/library for an Artifact with
a mana cost equal to half the number of Scrap counters removed and put that Artifact on to the battlefield.