原文To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Gust of Wind). The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
原文Once you announce that you're casting Gust of Wind, no player may take actions until the spell has been paid for. Notably, opponents can't try to change whether you control a creature with flying.