Shivara, Guardian of Unrest

Flying. Vigilance.
Whenever another creature you control dies,
exile it instead.
Pay X life, {t}: Return target creature that was
exiled using Shivara, Guardian of Unrest, where
X is that card's total converted mana cost. It
gains haste. Exile it at the beginning of the next
end step. If it would leave the battlefield, exile it
instead. Activate only as a sorcery.