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Counter target spell with mana value X. (For example, if that spell's mana cost is {3}{U}{U}, X is 5.)
Alternative costs, additional costs, cost increases, and cost reductions don't affect a spell's mana value.
If the target spell has {X} in its mana cost, include the value chosen for that X when determining the value of the {X} in Spell Blast's mana cost. For example, if you wish to counter Volcanic Geyser (a spell with mana cost {X}{R}{R}) whose X is 7, you'll need to choose 9 for Spell Blast's X and pay {9}{U}.
