Boros Keyrune 
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: Boros Keyrune becomes a 1/1 red and white Soldier artifact creature with double strike until end of turn. (It deals both first-strike and regular combat damage.)
Rulings:
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4/15/2013
Until the ability that turns the Keyrune into a creature resolves, the Keyrune is colorless.
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4/15/2013
Activating the ability that turns the Keyrune into a creature while it’s already a creature will override any effects that set its power and/or toughness to another number, but effects that modify power and/or toughness without directly setting them will still apply.
Legality:
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standard: Not legal
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future: Not legal
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frontier: Not legal
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modern: Legal
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legacy: Legal
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pauper: Not legal
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vintage: Legal
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penny: Legal
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commander: Legal
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duel: Legal
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oldschool: Not legal