Ashiok, Nightmare Weaver is a mythic Legendary Planeswalker — Ashiok card from Theros (THS), collector number 188. Current market price: $2.79 (foil $10.08), TCGplayer market prices via Scryfall.
+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.