Once each turn, you may pay 0 rather than pay the mana cost for a creature spell you cast from exile.
Retrieve Prey 1G
Sorcery — Adventure
Exile target creature card from your graveyard. Until the end of your next turn, you may cast that card.
Reverse Type:
Sorcery — Adventure
Exile target creature card from your graveyard. Until the end of your next turn, you may cast that card. (Then exile this card. You may cast the creature later from exile.)