On G+, I posted some work-in-progress icons for both a revision of Our Infernal Neighbors and the upcoming Ranks of the Undead. What you see here is the icon for the mummy chapter, a good segue into what I'm doing with the project.
See, when I got to the mummy chapter, I realized I'd put in more detail, compared to the other chapters. When I did the zombie-vampire and skeleton-lich tracks, I took the existing OD&D monsters as data points and filled in the "missing levels". I added a few interpretive twists, but not much. But when I did the mummy track, there was only one OD&D monster to work with, so I went to the movies instead. I made Kharis my low-level datapoint and Imhotep my high-level datapoint. That added a lot more backstory, a lot more flavor... but it makes the other undead tracks seem kind of unoriginal by comparison.
I need to insert more flavor. For the rotting undead, I made a passing reference to a bargain with "darkness" as their method of survival. I need to emphasize that more. I already mentioned plans to randomize the method of slaying a vampire permanently, and just finished writing that table. Lots of entries based on different vampire legends from different regions. The implication of the random method of permanent death is that it comes from the vampire's bargain with darkness. I'm also adding a Bargain with Darkness table for the lower pre-vampire levels. The undead gets a special power in exchange for a price, which at the moment are additional vulnerabilities similar to the vulnerability to garlic and mirrors. So, an Unhallowed might get the power to change into a rat, but can be turned by a ring of salt, exactly as a vampire is driven away by a cross. I even added "Counting Obsession" to the Price Paid table; scattering poppy seeds on the ground forces the undead with a counting obsession to gather and count them all, instead of attacking or chasing the victim, but it otherwise works using the Turn Undead roll.
For skeletal undead, I'd made a few references to their obsession with magical research, which seemed natural as something a proto-lich would do. I need to emphasize that more, possibly with a random table or two. My rewritten lich doesn't have the periapt of other versions, but I'm thinking of making that into an optional random feature (get one extra power through an arcane gem or amulet, but destroying it removes that power and possibly affects the skeletal undead itself.) I'm also toying with the idea of a random magical obsession table.
I haven't quite decided what to do to improve the spectral undead. One idea may have to do with random vengeances. Or I might find inspiration in interpreting them as an analog to another class. In a sense, vampires are the undead equivalent to fighters, and liches are magic-users. I rewrote mummies to be a little like clerics. So spectres and ghosts would be thieves, specializing in sneaking and surprise attacks. I'll have to think about that some more.