Orichalcos Stone
The Orichalcos Stone is the crystal that powers "The Seal of Orichalcos" in the Waking the Dragons arc, named for the legendary material "Orichalcum" featured in one of Plato's dialogues which also contained the characters "Critias" and "Timaeus". They were created by The Great Leviathan.
Features
To wield a fragment of the stone, the owner must be deemed worthy by it. If so, they are able to hold the stone in their hand and be granted great power. If they're not, their souls are taken by the stone and fed to the Great Leviathan. The stones are maintained by the darkness within the owner's heart, just like the Seal of Orichalcos magic card. But, if they overcome the darkness, the stone will shatter to pieces.
The people who are chosen by the stone gain power and mystical abilities that rival the Millennium Items. When the seal is active, it can materialize Duel Monsters and even control an Egyptian God. The seal acts like a force field that keeps the players inside and anyone else outside. When a duelist loses while the seal is active, his soul will be sealed inside the Great Leviathan. When the stone is thrown to the ground, it summons one or more Orichalcos Soldiers.
They also have the power to unlock and dispel the Seal of Orichalcos, but only from the outside. Other abilities include casting illusions, teleporting in a flash of light, and showing mental visions.