Creation myths regarding devils disagree in many particulars, but most fail to mention one incident - Asmodeus’s final fall from the upper realms. His route to the Pit remains a part of the Nessian landscape - a spiraling canyon called the Serpent’s Coil. Presumably, most of this corkscrewing tunnel was once underground, but over the eons it has collapsed in on itself, leaving a swirling incision on the surface. The canyon becomes deeper with each new curve until it reaches its endpoint, where it becomes incalculably deep. This spot is where Asmodeus sits to this day, scheming, commanding - and bleeding still.
Brutally repressed rumors suggest that there is more to Asmodeus than he admits. The story goes that the true form of Asmodeus actually resides in the deepest rift of Nessus called the Serpent's Coil. The shape seen by all the other devils of the Nine Hells in the fortress of Malsheem is actually a highly advanced use of the project image spell or an avatar of some sort.
The secret rift, supposedly formed by Asmodeus's plummeting body when he first arrived in the Nine Hells, spirals inward over the course of hundreds of miles. His titanic, miles-long form still rests here - and his wounds have yet to heal. His acid-black blood pools in the hollows of the rift, a substance fouler than foul.
From where fell Asmodeus? Was he once a greater deity cast down from Elysium or Celestia, or is he older yet, as the rumor hints? Perhaps he represents some fundamental entity whose mere existence pulls the multiverse into its current configuration. Nobody who tells the story of Asmodeus's “true” form lives more than 24 hours after repeating it aloud. But dusty scrolls in hard-to-reach libraries (such as Demogorgon's citadel in the Abyss) yet record this knowledge. Unless it is pure fancy, of course.