The Dark Dragon Potion was a neutral magical potion used in the episode "The Tale of the Dark Dragon".
This magical potion, works on people who aren't emotionally accepting parts of their personal
appearances. Also it can help them with emotional and psychical issues that they're experiencing with their bodies.
As seen at "Sardo's Magic Mansion", Sardo was as always trying to make a quick and easy sale. Therefore, he put out an advertisement. He promoted the product as a potion that could bring out the best in someone. Keith Saunders was mostly interested in this potion. He wanted it because a short time ago, he had survived a car accident which injured his leg leaving him with a limp and a leg brace. Also he felt unpopular, unwanted and insignificant among the rest of his schoolmates.
When he asked Sardo for it, Sardo reluctantly sold it to him for twenty dollars. Keith was advised to be very careful with it, and to only take one drop at a time. He tested the first drop in his bedroom, and it caused him excruciating pain and almost made him sick.
Then a few minutes later, it turned him into a much more handsome guy and it fully healed his leg (temporarily that is). This gave him the confidence to talk to other girls in his school. He became a suave and popular guy, while going under the alias K.C., However, he still wasn't accepting his real self.
The dosages of the potion seem to wear off after sleeping for a while. However, there is a major side effect. As a curse for someone doubting their real self, they slowly progress into becoming a hideous dragon like monster. The appearance is complete with sharp teeth, warts, scales and fangs. The side effects increase every time the potion is taken and wears off. Eventually, the transformation becomes so hideous, the person is no longer recognizable. Also whether or not they gain any type of powers is unknown.
As it was seen, the user's new preferred personal appearance can possibly become permanent. That is, if the potion is passed onto a new person, that they were emotionally close with. Keith's best friend Mariah, found out what he was doing. She broke into his locker and drank the entire potion, to make herself a beautiful girl perfect enough for him.
This made her a beautiful bombshell, she finally confessed her love to Keith. Then It turned that she too doubted her real her as well. Then rapidly, the curse was passed onto her. She begun to transform quickly, Keith huddled her in supporting comfort. He then rightfully admitted that he was the one supposed to change. Because he just wasn't happy, being the way he was anymore. Mariah confessed her feelings for him, and how she has always accepted him and always will. He then begged her not to go and cried tears straight from his heart.
Then suddenly, Keith and Mariah both realized they really did loved each other. Also they accepted each other for the way the really were, not the way they really weren't. When his tears dripped onto her, they both changed back to their old selves.
Keith then realized that the potion really did work. It brought out the best in him, to help him learn to accept himself for the way he is and to not care about what other people think. Also to finally let go of his feelings of doubt that he had ever since the car accident.