Transmutation | Magic: The Gathering
Formats Transmutation is Legal in
Official Oracle Text for Transmutation
Official Rulings for Transmutation
4/15/2013 : Effects that switch power and toughness apply after all other effects that change power and/or toughness, regardless of which effect was created first.
4/15/2013 : Switching a creature's power and toughness twice (or any even number of times) effectively returns the creature to the power and toughness it had before any switches.