Transmutation

Effects that switch a creature's power and toughness apply after all other effects, regardless of when those effects began to apply. For instance, if you target a 1/2 creature then give it +2/+0 later in the turn, it's a 2/3 creature, not a 4/1 creature.

Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature may become lethal if you switch its power and toughness during that turn.

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.

Note that the wording "Effects that alter the creature's power alter its toughness instead, and vice versa, this turn" has been removed.