Urza, Lord High Artificer

When Urza, Lord High Artificer centers the battlefield, create a 0/0 colorless Construct artifact creature token with "This creature gets +1/+1 for each artifact you control.
Tap an untapeed 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 it's mana cost.