I'm currently wanting to run a game in which the Shadowfell manifest is trying to overrun the multiverse and plunging it into shadow. However, upon reading about some D&D lore, it seems that Orcus wishes to do something similar, if not the same: make everything in the multiverse undead.

This then got me wondering about the relationship between the two. From what I understand, the Shadowfell is a realm of negative emotions (or lack thereof), shadow, and death. Orcus is not lord here, but instead of the Abyss. Is Orcus lord of the Abyss because he is a demon? Why isn't he lord of the Shadowfell, since it is *the* place of undeath?

I don't want my world to just be off-brand Orcus. I also want to make sense of this undeath thing, and why demons are doing it vs Shadowfell folk.