Atra, Guardian of Dreaming

Flying, Vigilance
Whenever a creature attacks you, you may pay {1}{u}. If you do, that creature doesn't untap during its controller's next untap step.
At the beginning of each player's end step, untap any number of creatures that player controls. If a creature was untapped this way, you gain 2 life.
{4}{b}: Destroy target untapped creature.