Eth'Rava, Harbinger of Decay

Eth'Rava, Harbinger of Decay's power and toughness are equal to the number of cards in your graveyard.
Whenever a creature dies, you may exile a card from your graveyard with converted mana cost equal to that of the creature that died. If you do, return that creature to the battlefield under your control, except it's a green Plant Horror with "When this creature dies, exile it instead."