Avacyn, the Tactician

Flash, flying
When Avacyn, the Tactician enters the battlefield, you may have creatures you control
gain indestructible until end of turn.
Whenever another creature you control dies,
you may exile Avacyn, the Tactician at the
beginning of the next end step. If you do,
put a card called "Avacyn, Baptized in Blood"
you own from outside the game onto the battlefield.