Dermot finds an old tome called
The Ghoul's Manuscript, where he discovers the following information:
. . . A colossal shadow appeared that was not wrought by anything in the room. It filled the portals from side to side, it towered above the lintel – and then, swiftly, it became more than a shadow: it was a bulk of darkness, black and opaque, that somehow blinded the eyes with a strange dazzlement. It seemed to suck the flame from the red urns and fill the chamber with a chill of utter death and voidness. Its form was that of a worm-shapen column, huge as a dragon, its further coils still issuing from the gloom of the corridor; but it changed from moment to moment, swirling and spinning as if alive with the vortical energies of dark aeons. Briefly it took the semblance of some demoniac giant with eyeless head and limbless body; and then, leaping and spreading like smoky fire, it swept into the chamber.
Mordiggian is the Great Ghoul. When he appears, all fire and heat is sucked into his swirling void-like body, instantly lowering the temperature by many degrees, and filling the area with a deathly cold and still air. All within the presence of the Great Ghoul are blinded by the weird changing and dazzling form of the necromantic god. Mordiggian attacks by engulfing victims, sucking away their life force, and dissolving their bodies. Nothing remains of the Charnel God's prey, and they are never seen again in the waking world or in the Dreamlands. However, Mordiggian does not appear to be especially malevolent and has been known to spare those who have not personally offended him or his followers (the ghouls); when a trio of Necromancers sneaked into the temple, the wizards were torn apart by the Ghoul priests, while Phariom and his newly revived wife were spared at Mordiggian's bidding. As one of the Necromancers said "Mordiggian's Wrath, though rarely loosed, is more terrible than any other deity. And it should not be thought by wise men to break into his sacred house." So while Mordiggian is attributed with immense powers of destruction, he is apparently a calm and benign deity.
Mordiggian's Priesthood consists exclusively of ghouls, though other races may offer up their dead to the Charnel God, but only as appeasement and not as actual worship, though some citizens of Zul-Bha-Sair, believed fully in him. The ghoul priests of Mordiggian cover themselves in long hooded robes of funeral-purple and silver skull-like masks. Although Mordiggian dwells within the Dreamlands, he is capable of entering the waking world, using the same grave-tunnels and tombs as his ghoul followers. It is likely that Mordiggian has some relationship with the waking lands. Proof of this is demonstrated by his worship in the city of Zul-Bha-Sair on the continent of Zothique in the distant future. There he is the only god since "from years that are lost to man's memory", and all who die in the city are offered to him as provender.
A different name for Mordiggian is Morddoth, mentioned as the dark god of the ghouls revered in the Valley of Hadoth by the Nile, in the ancient land of Altuas and in a time-lost continent likely matching with Zothique. So does the appearance fit with Mordiggian's one.