Mirror Universe

2007-09-16 When the life totals are exchanged, each player gains or loses the amount of life necessary to equal the other player's previous life total. For example, if player A has 5 life and player B has 3 life before the exchange, player A will lose 2 life and player B will gain 2 life. Replacement effects may modify these gains and losses, and triggered abilities may trigger on them.
2011-01-01 If an effect says that a player can't lose life, that player can't exchange life totals with a player who has a lower life total; in that case, the exchange won't happen.

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