Viren, High Mage of Katolis

Whenever another nontoken creature dies, create
a Treasure token. (It's an artifact with "{t},
Sacrifice this artifact: Add one mana of any
color.")
Sacrifice three Treasures: Target instant or
sorcery card in your graveyard gains flashback
until end of turn. The flashback cost is equal to
its mana cost. (You may cast that card from your
graveyard for its flashback cost. Then exile it.)