It as a certain unfinished feel to it, this sub.. But interesting, and original. Reminds me of "The Hell of Dry Bones". I have a great love of hells and pocket realms...
So, since you will be adding to this sub, I´ll recast my vote when it is finished.
I love hell dimensions. I really like your post. I understand, at least part of the reason, you feel this submission is unfinished. The ideas are basically all there although you left many details open for adjustments based on campaign needs. Let me just ask you several of the questions I had when I finished reading the post.
1. Obviously the Griz are intelligent humanoid life, but I'm unclear about the Render and the Boneslug. Are they intelligent enough to speak? have their own society? What did you have in mind for interracial relations (generally speaking of course)?
2. Are the falling corpses all the same kind of creature or are they radically different?
3. You spoke of a way out. Can your average dimension hopper leave using their ability or is there something keeping them here? Did you have a specific way out in mind?
4. What keeps a land mark of flesh around in a world of possibly starving scavengers?
Anyway that's enough for now. I have many ideas I'd be happy to share. Let me give it some thought and perhaps hear your answers to these questions and write something down for you. Again great ideas, nasty hell hole, and keep it coming.
Different kinds of corpses:
Every hundred years (or some distant time), a unique corpse falls. It is unique in the fact that it:
1. Mutates the eaters. This mutation could make colossal sized boneslugs or perhaps a form of lycanthropy in the Griz or Renders.
2. It has inedible, close to indestructible bones. One of these corpses produced the skull that makes up 'The Skull of the Leviathan'. This corpses' bones are the finest material to produce weapons, armor, or other structures.
3. Not quite a corpse. Where almost everything that falls is dead, this one is alive, Perhaps it's critically injured from the fall, the titanic beast gets up and is capable of action for a time. The climate and lack of food will undoubtedly kill it within the space of a few days if the scavengers don't kill it first.
A way out:
1. Veshpether is actually hollow. At the very peak, there is an opening, which one can climb into and drop through the whole plane of Corpsefall and land in another hell dimension which lies below. Without the ability of flight, this is an extremely risky venture.
2. Elder Boneslug. Hidden in a strange part of the land (perhaps the Shunned Lands) is a gigantic boneslug. This boneslug has unusual markings and seems to be immobile. Visitors will find that it can move and is exceptionally hungry. The boneslug bowel is a dimensional door that will send the person the boneslug eats into a world between worlds type of location. Slaying the Elder Boneslug will destroy the portal and all hope of escape.
3. Semi-frequent dimensional visitors: A certain greater demon has taken a liking to this location and uses Corpsefall to punish his minions in their failures. A desperate and charismatic person may be able to hitch a ride out of Corpsefall after signing a pact with the demon. A devious person may be able to sneak through any portals when the punished minion is welcomed back home.
4. If one could combine the magic of flight with prophecy. One could figure out where & when the next corpse will fall and be able to fly up through the portal before it closes. This upper dimension is probably another hell dimension, where the reptile beings are continuously clothed in flesh and tortured to death. With their 'used' up bodies being dropped into Corpsefall.