This achievement is story related and cannot be missed.
This achievement can be earned in the fifth world "Mystical Pique" on the first level "Moseying the Mountain." On the 2nd stage of the level you will see Helena trapped by a Darktoon who will try to escape. After swinging and wall jumping you'll have the enemy cornered on the ceiling. Wait for the Darktoon to run in the middle opening, then jump and kick it to free the Nymph. You will be awarded a special ability and 15G!