Time Bomb

Ultimate - (You may only cast this card if you
control a creature named Skye, the Twilight
Assassin. Exile this spell once it resolves. When
the associated creature dies, if this card is in exile,
shuffle that creature and this card into your library.)
Choose one creature, destroy the rest. Target
player gets a poison counter for every 3 creatures
that are destroyed this way.
Time's ticking.