If a creature’s power is less than 0 when it’s doubled, doubling that creature’s power instead means that the creature gets -X/-0, where X is the difference between 0 and its power. Similarly, if its toughness is less than 0 when doubled, it gets -0/-X. If one characteristic’s value is negative but the other isn’t when both are doubled, it gets -X/+Y or +X/-Y, as appropriate.
July 12, 2019 · Core Set 2020
When life totals are exchanged, each player gains or loses the amount of life necessary to equal the other player’s previous life total. Replacement effects may modify these gains and losses, and triggered abilities may trigger on them. A player who can’t gain life can’t be given a higher life total this way, and a player who can’t lose life can’t be given a lower life total this way (see rules 119.7–8).
May 3, 2019 · War of the Spark
When life totals are exchanged, each player gains or loses the amount of life necessary to equal the other player’s previous life total. Replacement effects may modify these gains and losses, and triggered abilities may trigger on them. A player who can’t gain life can’t be given a higher life total this way, and a player who can’t lose life can’t be given a lower life total this way (see rules 118.7–8).
January 25, 2019 · Ravnica Allegiance
When life totals are exchanged, each player gains or loses the amount of life necessary to equal the other player's previous life total. Replacement effects may modify these gains and losses, and triggered abilities may trigger on them. A player who can't gain life can't be given a higher life total this way, and a player who can't lose life can't be given a lower life total this way (see rules 118.7-8).
April 27, 2018 · Dominaria
When life totals are exchanged, each player gains or loses the amount of life necessary to equal the other player’s previous life total. Replacement effects may modify these gains and losses, and triggered abilities may trigger on them. A player who can’t gain life can’t be given a higher life total this way, and a player who can’t lose life can’t be given a lower life total this way (see rules 118.7–8).
September 30, 2016 · Kaladesh
rule 701.10c not present in this release
September 30, 2011 · Innistrad
If a creature fights itself, it deals damage equal to its power to itself twice.
June 17, 2011 · Commander 2011
Some effects instruct a player to “play” with a certain aspect of the game changed, such as
April 1, 2011 · Duel Decks: Knights vs. Dragons
Some effects instruct a player to "play" with a certain aspect of the game changed, such as "Play with the top card of your library revealed." "Play" in this sense means to play the _Magic_ game.
February 4, 2011 · Mirrodin Besieged
Some effects instruct a player to “play” with a certain aspect of the game changed, such as “Play with the top card of your library revealed.” “Play” in this sense means to play the Magic game.
October 1, 2010 · Scars of Mirrodin
Some effects instruct a player to “play” with a certain aspect of the game changed, such as
February 1, 2010 · Worldwake
Some effects instruct a player to "play" with a certain aspect of the game changed, such as "Play with the top card of your library revealed." "Play" in this sense means to play the _Magic_ game.