The final crystal's powers were not revealed until the near end of the series. In Episode 64: "L.B.'s Wedding", Gimmick is trying restlessly to use his scientific knowledge to discover the powers of the sixth crystal, maybe as a means of showing off to the Illiops of Rillionia what a great proffessor he is. Meanwhile, Tweeg has made his way onto the shores of Rillonia and manages to find Teddy's home. While he waits outside the window, Gimmick comes inside to have something to eat before continuing with his experiments.
In the middle of lunch, Grubby knocks over a cup of orange juice which splashes all over the crystal. He fails to notice the effects of such an action as the crystal takes flight and slowly floats out the window into Tweeg's hands. Just as Tweeg is beginning to think he has the ticket to getting back into M.A.V.O., the crystal continues to fly into the airthis time with a big green grunge holding onto it.
The trio hear his screams and make their way to the Airship in an effort to save Tweeg and the crystal. Gimmick quickly deduces that the citric acid (Vitamin C) from the orange juice has activated the crystal's ability of flight. He also includes that when the acid on the crystal evaporates, it will fall, and so will Tweeg.
And so the powers of all the original six crystals have been revealed. Unfortunately, the powers of the sixth crystal were only used in Episode 64, and quickly reviewed in the final episode of the series.
Character Profiles I Crystals I The Quiz I Inventions I Image Sources I Episode Guide