Memento Mori

If this spell rebounded, it can't be countered.
You gain 1 life for each creature you control. If this spell was cast from exile, all creatures lose indestructible until end of turn, then destroy all creatures.
Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)