Super-Special Tummy Tonic
At the beginning of her story in the Twist League, Penny creates an elixir with the desire of using it to enhance her voice and become a pop star. She then tests it on her grandfather, Dr. Crygor, and it is successful in making his voice higher in pitch, but also puts him in a condition of extreme stomach pain.
Penny, remembering her Super-Special Tummy Tonic, gives it to her grandfather to use as a cure for the Tonally Transformative Elixir. Although it reduces Dr. Crygor's stomach pains, it does not fix his higher-pitched voice, which is suggested to be a permanent effect.
Regardless, Dr. Crygor speaks with his regular voice in future scenes, suggesting that the effects might have gone away on their own or been cured by another potion.