The Swan Computer

This artifact enters with 4 time counters on it.
At the beginning of each player's upkeep,
untap this artifact and remove a time counter from it. That player draws a card.
{1}{t}, tap target creature you control: put a
time counter on this artifact. Any player may activate this ability during their turn.
At the beginning of your end step, if this artifact has no time counters on it, exile all
nonland permanents.