Kiera, Prodigy of House Fura

Whenever you cast an instant or sorcery spell
from your hand, exile cards from the top of your library until you exile an instant or sorcery card that costs less. You may cast that card without paying its mana cost until the beginning of your next end step. Put the rest of the exiled cards on the bottom of your library in any order.
{u}{r}, {t}: Change the targets of target spell or ability with a single target.