The Millennium Calendar 
Legendary Artifact
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.
Legality
standardLEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL