The third crystal, if you haven't figured out already, has the power to make you invisible. Our heroes found this out when Gimmick was doing an experiment with them. He placed the crystal on a tray and shined a flashlight on it, the beam refracted off the crystal and hit the other five, causing them to disappear. Then, Teddy told Gimmick to reverse the crystal on the tray and shine the light again. When he did, the other crystals reappeared.
It also made Gimmick's fireplace disappear, and helped Teddy, Grubby, and Gimmick get Fuzz back when he was kidnapped by Tweeg and L.B. They were scared to death when they saw a flying fob (Teddy, Grubby and Gimmick were holding them up and walking him out the door).
Other Places to Find the Invisibility Crystal
Episode 5: Escape From the Treacherous Mountains
Episode 8: Tweeg's Mom
Episode 10: The New M.A.V.O. Member
Episode 27: The Crystal Book
Episode 30: Tweeg Joins M.A.V.O.
Episode 33: Captured
Episode 36: Leakee Lake
Episode 37: The Third Crystal
Episode 63: On the Beaches
Episode 65: The Mystery Unravels
Character Profiles I Crystals I The Quiz I Inventions I Image Sources I Episode Guide