Princess Serenity, Reborn

This spell can't be countered and costs {x} less
to cast, where {x} is the number of Sailor Senshi
on the battlefield.
As long as Princess Serenity, Reborn is on the battlefield, you can't lose the game and your opponents can't win the game.
{t}{6}: Exile all nonland black permanents on the battlefield or in any graveyard.