Desperate Gambit

Oracle Text

Choose a source you control and flip a coin. If you win the flip, the next time that source would deal damage this turn, it deals double that damage instead. If you lose the flip, the next time it would deal damage this turn, prevent that damage.

Card Rulings

10/4/2004 The coin is flipped during resolution of this spell, so you know in advance what will happen when the source deals damage the next time.
4/1/2008 The chosen source may be a permanent, a spell on the stack, or anything referred to by something on the stack (such as a Prodigal Pyromancer that’s left the battlefield while its ability is still on the stack)