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15/07/06

If an opponent casts a spell with X in its mana cost, the converted mana cost of that spell takes the value of X into account. If you reveal a card with X in its mana cost, X is 0. For example, if your opponent casts Blaze with X=1, Counterbalance will counter that spell if you reveal a card with converted mana cost 2, but it won’t counter that spell if you reveal a Blaze of your own.