Exile the top X cards of your library. For each instant and sorcery card with converted mana cost X or less among them, you may cast that card without paying its mana cost. Then put all cards exiled this way that weren't cast into your graveyard.
10/1/2012 You cast the cards one at a time, choosing modes, targets, and so on. The last card you cast will be the first one to resolve.
10/1/2012 When casting an instant or sorcery card this way, ignore timing restrictions based on the card’s type. Other timing restrictions, such as “Cast [this card] only during combat,” must be followed.
10/1/2012 If you can’t cast an instant or sorcery card, perhaps because there are no legal targets available, or if you choose not to cast one, it will be put into your graveyard.
10/1/2012 If you cast a card “without paying its mana cost,” you can’t pay alternative costs such as overload costs. You can pay additional costs such as kicker costs. If the card has mandatory additional costs, you must pay those.
10/1/2012 If a card has in its mana cost, you must choose 0 as its value.