Boltfire

“Flashforward [cost]” means “You may cast this card from exile by paying [cost] rather than paying its mana cost” and “If the flashforward cost was paid, put this card on the bottom of its owner’s library instead of putting it anywhere else any time it would leave the stack.”

To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashforward cost) you’re paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.

A spell cast using flashforward will always be put on the bottom of its owner’s library afterward, whether it resolves, is countered, or leaves the stack in some other way.