As you approach...
The cord behind the robed figure appears to be some sort of umbilical cord connected to the skull through the hood. The body is indeed Corvus, In a cultist's robe he is completely unresponsive, and his eyes have gone white as milk. The quivering cord grows taught as you draw nearer and a great shapeless shadow spreads over the table as An immense glistening form uncoils itself from the slimy cobbles of the room's vaulted ceiling and descends with a slow viscous motion on ropes of faintly glowing alchemically tainted mucus. The sheen of several multifaceted eyes scrutinizes you from the darkness above.
Corvus: YOU you are the fools who interrupt my metamorphosis! My second alchemical masterpiece..! Oh It was folly to have thought my cabinet would be your tomb! No this is the way it must be! That such delicious wills have sought me out in my own sanctum like flies blundering in a web! I shall paralyse your minds and then feed upon you when I emerge a splendid winged thing! the divine likeness of Thlesothaggua!
The creature is about the length of 4 warhorses end to end, and resembles a gigantic leach and (nature check 15) the larval form of a caterpillar interrupted in the midst of its metamorphosis. It's back is covered in translucent chitin plates and rudimentary folded wings. through the plates you can see sparks of arcane light as boils arise from the creatures skin, fill with a glowing alchemical substance, and then erupt in pale blue pus that oozes through the plating. It's mouth is formed of 5 detached jaws webbed together by slimy membranous tissue.