To double a creature’s power, that creature gets +X/+0, where X is that creature’s power as the spell or ability that doubles its power resolves. Similarly, an effect that doubles a creature’s toughness gives it +0/+X, where X is that creature’s toughness. Doubling a creature’s power and toughness gives it +X/+Y, where X is its power and Y is its toughness.
April 27, 2018 · Dominaria
When control of two permanents is exchanged, if those permanents are controlled by different players, each of those players simultaneously gains control of the permanent that was controlled by the other player. If, on the other hand, those permanents are controlled by the same player, the exchange effect does nothing.
September 30, 2016 · Kaladesh
rule 701.10b not present in this release
September 30, 2011 · Innistrad
If a creature instructed to fight is no longer on the battlefield or is no longer a creature, no damage is dealt. If a creature is an illegal target for a resolving spell or ability that instructs it to fight, no damage is dealt.
June 17, 2011 · Commander 2011
To play a card means to play that card as a land or to cast that card as a spell, whichever is
February 4, 2011 · Mirrodin Besieged
To play a card means to play that card as a land or to cast that card as a spell, whichever is appropriate.
October 1, 2010 · Scars of Mirrodin
To play a card means to play that card as a land or to cast that card as a spell, whichever is
February 1, 2010 · Worldwake
To play a card means to play that card as a land or to cast that card as a spell, whichever is appropriate.