Beyond Power

Altered (This spell must be cast using void mana)
Empty -Sacrifice 3 Demons - (You may cast this card for its empty cost. If you do, exile it as it resolves. During your precombat main phase, if an opponent cast no spells last turn, you may cast the exiled card without paying its mana cost. Empty only as a sorcery.)
Target opponent loses X life and you gain X life where X is the number of cards in your graveyard.