This episode is also directly in line with the LD Storyline leading up to Story Two.
After searching through his spell books, Gargamel discovers a page about Mother Nature's legendary Wheel of Creation, which is what determines what species any new life form will be upon their arrival into the world. With his sidekicks, he ventures to Mother Nature's home when she is away and decides to switch the "Human" marker with something else. In doing so, he upsets the balance of all life, so the wheel randomly switches every marker to account for the villain's change. Once all is settled, the Smurfs become human, humans become sprites, merfolk are now Smurfs, etc. Will the natural order be restored before the Smurf Village is destroyed? How will the humanized Smurfs survive if their home is only accessible by true Smurfs?