Guile | Magic: The Gathering
Formats Guile is Legal in
Official Oracle Text for Guile
If a spell or ability you control would counter a spell, instead exile that spell and you may play that card without paying its mana cost.
When Guile is put into a graveyard from anywhere, shuffle it into its owner's library.
Official Rulings for Guile
10/1/2007 : Exiling the spell is mandatory. Casting it is not.
10/1/2007 : A spell exiled this way was never actually countered.
10/1/2007 : If a spell or ability you control attempts to counter a spell that can't be countered, it doesn't. Since the spell wouldn't be countered, Guile's ability has no effect on it. The spell will continue to resolve normally.
10/1/2007 : The last ability triggers when the Incarnation is put into its owner's graveyard from any zone, not just from on the battlefield.
10/1/2007 : Although this ability triggers when the Incarnation is put into a graveyard from the battlefield, it doesn't *specifically* trigger on leaving the battlefield, so it doesn't behave like other leaves-the-battlefield abilities. The ability will trigger from the graveyard.
10/1/2007 : If the Incarnation had lost this ability while on the battlefield (due to Lignify, for example) and then was destroyed, the ability would still trigger and it would get shuffled into its owner's library. However, if the Incarnation lost this ability when it was put into the graveyard (due to Yixlid Jailer, for example), the ability wouldn't trigger and the Incarnation would remain in the graveyard.
10/1/2007 : If the Incarnation is removed from the graveyard after the ability triggers but before it resolves, it won't get shuffled into its owner's library. Similarly, if a replacement effect has the Incarnation move to a different zone instead of being put into the graveyard, the ability won't trigger at all.