Regenerate on moonlight
When a moonlight creature with regenerate transforms (after having taken damage), it appears as though the game "knows" what its boosted toughness should be, but instead resets the toughness to the transformed creature's value and doesn't further heal (even after taking damage, despite the card still having the regenerate text on it).
If you cast a second regenerate on the creature, it will magically fully heal to its fully buffed toughness again.
e.g. regenerate & giant growth on estwald outcast (6/5) that then takes 4 damage (6/1) and transforms will turn into a 7/3 sneak regenerate. But won't heal (even back to 3) if it takes damage. Cast regen again, though, and it'll bounce back to 8/7 at end of turn