When reading in the DMG about the Nine Hells, I got curious what Asmodeus' powers actually might be. I was assuming I would find this in the MM, but I couldn't find even a hint. The section about the devils mentions a lot about the Nine Hells and who is ruling where and so on.
But there are no stats for any of them, just stats for their vassals. And I could also see no hint of how I might modify the "common" devils to represent the Dukes nor anything else.
So is this all up to me to create the stats of well-known lore "bosses"?
Or am I just overlooking some info about how to extract this from or modify common monsters to form important known ones?