Instant, U (1) Counter target spell if no mana was spent to play it. "There is no shortcut to work done true and well. The Creators learned this to their sorrow, the first time they made the world."
—Githri the Prisoner
Illus. Brian Despain
It can target any spell. The amount of mana spent is checked only on resolution. [Future Sight FAQ 2007/05/01]
The mana cost may be more than zero as long as an alternate cost or a cost reduction was used to avoid paying it, or if it is a copy of a spell so no mana was pad when playing it. [Future Sight FAQ 2007/05/01]