Rule 810.7b

Any one-shot effect that refers to the “defending player” refers to one specific defending player, not to both of the defending players. The controller of the effect chooses which one the spell or ability refers to at the time the effect is applied. The same is true for any one-shot effect that refers to the “attacking player.” Any characteristic-defining ability that refers to the “defending player” refers to one specific defending player, not to both of the defending players. The controller of the object with the characteristic-defining ability chooses which one the ability refers to at the time the nonactive players become defending players. If that time has already occurred, that player makes that choice as the object enters the battlefield or gains the ability. All other cases in which the “defending player” is referred to actually refer to both defending players. If the reference involves a positive comparison (such as asking whether the defending player controls an Island) or a relative comparison (such as asking whether you control more creatures than the defending player), it gets only one answer. This answer is “yes” if either defending player in the comparison would return a “yes” answer if compared individually. If the reference involves a negative comparison (such as asking whether the defending player controls no black permanents), it also gets only one answer. This answer is “yes” if performing the analogous positive comparison would return a “no” answer. The same is true for all other cases that refer to the “attacking player.”

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