Graygem
The Graygem or Graystone is a powerful ancient artifact in the D&D setting of Dragonlance. It is said to be responsible for the creation of many different races and monsters via magical mutation.
The trickster god Hiddukel tricked the Dwarven god Reorx into forging the Graygem. It was then placed on the moon Lunitari for safekeeping, where it stayed until a Tinker Gnome, in true gnomish fashion, invented a Self-Propelled Lunar Extension Ladder, allowing him to climb up to the moon and steal the jewel. No really, we're not kidding. It has been stated across various splatbooks that the gnome actually built this device around a magical artifact given to him by Reorx, so it has the magic doing the heavy lifting.
Unfortunately, the gnome lost his grip on the Graygem as he was climbing back down and the jewel fell down to Krynn, where it caused all sorts of mischief by radiating powerful chaos magic. This led to the creation of many, many different races, especially those that look like somebody fused two different species together... because that is exactly how they started. The Graygem is most well-known, however, for leading to the Tinker Gnomes to abandoning the mainland of Ansalon and to the transformation of about two thirds of the race into the Dwarf and Kender races.
After that, it vanished from history... until it reappeared some time after the Third Dragonlance War. That as when the gem was broken and Chaos, who is basically Krynn's Ao, but an active dick, was released. He promptly tried to rip the world apart, forcing everybody to work together to beat him. Amazingly, Chaos is actually not as Mary Sue as Ao, so he genuinely lost the fight... not that it was easy!