Crookclaw Transmuter

• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2021-03-19
  Official Ruling
  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.
• WWizards of the Coast2021-03-19
  Official Ruling
  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.
• WWizards of the Coast2021-03-19
  Official Ruling
  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.

Rulings via Scryfall