Distended Mindbender [Eldritch Moon Prerelease Promos]

Emerge {5}{B}{B} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's converted mana cost.)
When you cast this spell, target opponent reveals their hand. You choose from it a nonland card with converted mana cost 3 or less and a card with converted mana cost 4 or greater. That player discards those cards.