Spellshift

Instant, 3U (4)
Counter target instant or sorcery spell. Its controller reveals cards from the top of his or her library until he or she reveals an instant or sorcery card. That player may play that card without paying its mana cost. Then he or she shuffles his or her library.
Illus. Stephen Tappin

Crystal Keep Rulings Summaries

• If the targeted spell cannot be countered, it remains on the stack and the rest of this spell's effects occur. [Planar Chaos FAQ 2006/12/13]
• If the revealed card isn't played, it gets shuffled back into the library. [Planar Chaos FAQ 2006/12/13]
• If there are no Instants or Sorceries in the library, the whole library is revealed and then shuffled. [Planar Chaos FAQ 2006/12/13]

Format Legality	Legal in Vintage, Legacy, Extended Banned in Standard
Printings (1/9)	Planar Chaos (Rare)