The Gem Dragon (also known as the Gem of ultimate power) is presumably a Corrupted Gem that was found within Hoppy and Hopper's world.
Description[]
The Gem Dragon resembles an eastern dragon, with colors matching the gemstone it's based off. It has deer antlers, rabbit-like ears, and canine-like teeth.
The Gem Dragon can apparently deliver huge amounts of power to whoever it wishes, shown when it powered up Ringo to successfully make the others forget about it and focus on Ringo.