Beseech the Mirror

Sorcery {1}{B}{B}{B}

Bargain (You may sacrifice an artifact, enchantment, or token as you cast this spell.) Search your library for a card, exile it face down, then shuffle. If this spell was bargained, you may cast the exiled card without paying its mana cost if that spell's mana value is 4 or less. Put the exiled card into your hand if it wasn't cast this way.