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 cast that card without paying its mana cost. Then he or she shuffles his or her library.¹
Illus. Stephen Tappin

Gatherer Card Rulings [Nov 2009]

• 2/1/2007: If the targeted spell can't be countered, it remains on the stack and the rest of Spellshift's effect continues to happen.
• 2/1/2007: If the revealed instant or sorcery card isn't cast, it gets shuffled back into the library.
• 2/1/2007: If there are no instant or sorcery cards in the player's library, the entire library is revealed and then shuffled.

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