Doomsday

At the beginning of each player's end
step, add a doomsday counter onto
Doomsday unless you pay {p/c}.
Doomsday deals 1 damage to each player
for each doomsday counter on Doomsday.
(Players can interact with the doomsday counter.)
({p/c} can be paid with either {1} or 1 life.)