Zilean, The Chronokeeper

When Zilean enters or attacks, scry 3 and create a Timebomb token at the beginning of your next upkeep with "{t} Sacrifice this artifact. When you sacrifice this artifact, draw 1, deal 1 damage to all opponents and creatures opponents control, and sacrifice all other Timebombs."

Level up (When you've sacrificed 2 or more Timebombs while Zilean was on the battlefield, grant Zilean +1/+1 and "You may cast cards that entered the graveyard last turn.")