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If 
was spent to cast this spell, you may have target creature get -3/-3 until end of turn. If 
was spent to cast this spell, you may have target creature get +3/+3 until end of turn. (Do both if was spent.)
Read from the rules text. A card that enables a keyword makes or is the thing; a card that rewards it gets better when you have it. Two cards interact when one enables what the other rewards.
