Lily the Harbinger of Sorrow

Fairy Immortality: If this creature would die
or be exiled, it enters the command zone instead. It
costs {b}{b} more to cast for each time it has entered
the command zone
Flying
When Lily the Harbinger of Sorrow enters the battlefield, destroy target creature an opponent controls with mana cost equal to or less than the
amount of {b} spent to cast it
It ends