The Millennium Calendar (Extended Art) - The Lost Caverns of Ixalan: (Extended Art)

Whenever you untap one or more permanents during your untap step, put that many time counters on The Millennium Calendar.
, : Double the number of time counters on The Millennium Calendar.
When there are 1,000 or more time counters on The Millennium Calendar, sacrifice it and each opponent loses 1,000 life.