Tonally Transformative Elixir
During the prologue of Penny's stage in the Twist League, she creates the elixir with the intention of using it to enhance her voice and become a pop star. Dr. Crygor questions this but promises to support her no matter what. Penny then uses him as a test subject and pours the potion down his throat, which makes his voice much higher in pitch. He agrees that the effects on his voice are impressive, but the taste is terrible, and then goes into a state of extreme stomach pain.
Penny remembers her Super-Special Tummy Tonic, which she uses as an antidote to cure the elixir. This causes Dr. Crygor's stomach pains to ease, and she asks if there are any improvements she could make, to which he replies to work on the painful side effects. He then asks her when the effects are supposed to wear off, to which Penny giggles nervously, implying that the effects might be permanent.
Despite this, during the future scenes Dr. Crygor appear in, he speaks with his regular voice, meaning that the effects might be temporary after all.
Penny is shown to have used this elixir off-screen in the intro cutscene for the "Dancing Team" story.