Riddleborn Sphinx

Secretive - When Riddleborn Sphinx enters the battlefield, exile three cards from your graveyard
in a face-down pile, and shuffle that pile. (You
may look at those cards any time.)
{w}{u}{b}, Choose a face-down card you own in
exile and put it on top of your library: Target opponent chooses a card name. Then reveal the
top card of your library. If it's a card with the
chosen name, that player draws a card. Otherwise
that player sacrifices a creature.