Ashiok, Nightmare Weaver

Oracle Text

+2: Exile the top three cards of target opponent's library.

−X: Put a creature card with converted mana cost X exiled with Ashiok, Nightmare Weaver 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.

Card Rulings

9/15/2013 Ashiok’s second ability refers to any creature card exiled because of Ashiok’s first or third ability.
9/15/2013 Ashiok’s second ability doesn’t target any creature card. You choose which creature card to return when that ability resolves, but you must choose one with converted mana cost equal to the value you chose for X when activating the ability.
9/15/2013 If Ashiok leaves the battlefield, and later another Ashiok enters the battlefield, it is a new object (even if the two were represented by the same card). Creature cards exiled by the original Ashiok can’t be put onto the battlefield by the second ability of the new Ashiok.
9/15/2013 If you put a creature card with bestow onto the battlefield, it will be a creature on the battlefield, not an Aura.
9/15/2013 If you put a creature card with in its mana cost onto the battlefield, the value of that X is 0.