Halcyon, the Sky City

When Halcyon, the Sky City enters the battlefield, you get {e} (an energy counter).
At the beginning of your upkeep, sacrifice Halcyon, the Sky City unless you pay {e}.
{t}: Add {w} or {u}.
{3}{w}{u}, {t}: Return target artifact card or Artificer creature card from your graveyard to your hand.