Sky Fortress Damocles

Sky Fortress Damocles has indestructible as long
as it's untapped.
At the beginning of each upkeep, put a charge
counter on Sky Fortress Damocles. Then if Sky Fortress Damocles has twenty or more charge counters on it, you win the game.
{4}, {t}, Remove four charge counters from Sky
Fortress Damocles: Exile all nonland permanents target player controls.