666 (Trihexa)

666 (Trihexa) is a legendary being known as the Apocalyptic Beast and is stated to be a being that is on par with Great Red.

History
At some point in the past, the God from the Bible confirmed the existence of 666 that was thought to be unknown and placed thousands of seals on 666, sealing it at the "end of the world".

The Legend of Oppai Dragon and his Lively Companions
666 was mentioned in Volume 16 by Rizevim who reveals his goal to unseal Trihexa that was previously sealed by the deceased God From the Bible at the "end of the world" using the Sephiroth Graal and Incinerate Anthem.