Ashiok, Nightmare Weaver

Legendary Planeswalker — Ashiok — {1}{U}{B}

+2: Exile the top three cards of target opponent's library. −X: Put a creature card with mana value X exiled with Ashiok onto the battlefield under your control. That creature is a Nightmare in addition to its other types. −10: Exile all cards from all opponents' hands and graveyards.