They were clearly Xan.
Shadowlands IS a physical place.
People don't seem to read this thread. The Shadowlands and Rubi-Ka are the SAME planet. When all that mystical BS went down part of Rubi-Ka was ripped out and throw into its own pocket of dimension, creating the Shadowlands.
The Beast as not PUT there but rather Sealed there. By who? By what? I don't know. I assume the Kyr'Ozch. Obviously.
The Beast's name is Abad-don. Abaddon means quite literally "Lucifier," "Satan," or "Devil."
The Fisher King, which was the original form of Abad-don, was obviously the God entity. . .
Arthur lost his mind, as did the eight heros, and this became Abad-don. He went and absorbed leaders of the plane and took in twenty souls to become his body.