Urza, Lord High Artificer

When Urza, Lord High Artificer enters the
Battlefield, create a 0/0 colorless Construct
artifact creature token with "This creature
gets +1/+1 for each artifact you control."
Tap an untapped artifact you control: Add {u}
{5}: Shuffle your library, then exile the top
card. Until end of turn, you may play that card without paying its mana cost.