The Millennium Calendar — The Lost Caverns of Ixalan Promos #257p

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.