Aetherbound Clockwork

When Aetherbound Clockwork enters the battlefield, you get {e}{e}.
At the beginning of your upkeep, sacrifice Aetherbound Clockwork unless you pay {e}.
Aetherbound Clockwork's power and toughness are each equal to the amount of {e} you have.
Artificial life has a cost, despite what all of Kaladesh may have you believe.