Sierra, Time's Chosen

{1}{u}, {t}, Discard a card: 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.)
Whenever you cast an instant or sorcery spell, if you have cast at least four instant or sorcery spells this turn, take an extra turn after this one.