Mnemosyne the Living Memory

Mnemosyne costs X less to cast, where X is the
number of creatures that died this turn.
When Mnemosyne attacks, you may cast spells
from your graveyard until end of turn. Exile any
spells cast this way.
{1}{b/r}, Discard a card: Draw a card.
Rebirth - 3{b}{r}{g}, 5