Phantom Ruby

The Phantom Ruby, also known as the Mysterious Gemstone, is an object that appears in Sonic Mania. It is a gemstone that contains incredibly powerful energy.

Sonic Mania
The Phantom Ruby is discovered on Angel Island by the Hard-Boiled Heavies, and they use it's power to send Sonic the Hedgehog, Miles "Tails" Prower and Knuckles the Echidna to Green Hill Zone. They eventually give it to Dr. Eggman who abuses its power further.