Nahiri, Zendikar's Vindicator

{w}{r}, Sacrifice a creature: Nahiri, Zendikar's Vindicator gains Double Strike until end of turn. If the sacrificed creature was a Vampire or Eldrazi, add {w}{r} to your mana pool.
Whenever you sacrifice two creatures you don't own, exile Nahiri, Zendikar's Vindicator and then return it to the battlefield transformed.
"For denying me in my time of peril, it shall be cast upon your creation, Sorin."