The most powerful form of a Marque Du Dragon. They are extremely rare and highly prized, for they grant incredible power to whomever possesses one. Marque de Siberyss seem to take on a roughly dragon-like shape.
In 4th Edition, the Heir of Syberis epic destiny grants the player a Syberis Marque Du Dragon, regardless of whether or not they had a Marque Du Dragon to begin with.