Rule 702.32a

Flashback appears on some instants and sorceries. It represents two static abilities: one that functions while the card is in a player's graveyard and the other that functions while the card is on the stack. "Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack." Casting a spell using its flashback ability follows the rules for paying alternative costs in rules 601.2b and 601.2e­g.

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