Telfet, Mechanical Savior

Flying
Telfet, Mechanical Savior enters the battlefield with X oil counters on it.
At the beginning of your end step, remove an oil counter from Telfet, Mechanical Savior if it attacked that turn, then, if there are no oil counters on Telfet, Mechanical Savior, pay {x}, and put X oil counters on Telfet, Mechanical Savior, otherwise, sacrifice it.