Firstly, some general points: why have multiple "contributors" to this found-text style book if they all speak the same and with a Sigil accent? Why are they all uniformly urban and colloquial? Also, stop saying "some folks/scholars/whatever believe", I mean, fuck, this is supposed to be a book by demon experts, act like it. On the flip side though, these guys know way too much. Why do they know the identities of the Dark Eight? The ins and outs of the political structure? You can't be simultaneously a blabbering idiot and omniscient with regards to this impenetrably Byzantine (but apparently entirely simple and single page illustrationable) society. This book would be 1/3 the size if you cut out all the waffling, but then that's the 90s for you.
Origin of the Species
Nope, none of this chapter, all flimflam. The Baatzu are a self shaping race. The Nupperibo (effectively, along with the Lemures, the Baatzu peasantry) are the only natural form, springing up from the body of the plane. Before the fiends knew how to drag themselves up to godhood by their bootstraps, this was it. A flat hell full of angry little fat men and Gods.
The Lemures represent the first steps of malleability. Just look at them.
Station to Station
The hierarchy adheres to a totally alien logic, is inconceivably convoluted, and above all is not understood by non-Baatzu except in the most vague and general terms.
The Process of Promotion
This chapter has some of the best bits in the book. It explains how each promotion/transformation has a specific method to it. For instance, a lemure chosen to become a spinagon fights in a big battle royale until one is left. The winner is carted off and skinned, whereby the foetally forming spinagon inside is revealed. Hoorah!
Most interestingly is the one where kocrachons rearrange the fiends bones to form the new shape, adding another syllable to his name which is written on his bones that are made of not-bone. I propose to finish this idea the book almost had:
BAATZU BONES AND TRUE NAMES
The baatzu don't have bones in the sense we know them. Theirs are angular and metallic, obviously man-formed and hammered. On every surface is writing which, if arranged and read correctly, will spell the fiends true name. Short of getting them to tell you this is pretty much the only way of learning it, but arranging a few hundred bones in the correct order isn't easy.
As the fiend ages and changes form their frame is enlarged and complicated. This is less a matter of bigger is better and more a practical result of just having more bones in their bodies on which to hold their ever lengthening name.
Baatzu green-steel? That's demon bones, forged into weapons. THAT'S why you never see it sold, and why it hurts demons, and is cool. Also, demon weapons like in Warhammer are now a thing. Trap the spirit of a big powerful demon in a bunch of weapons.
Bodily Form and Function
Another gumpfy chapter. Who took the time to figure out a Baatzu's pineal glad is big? Or their long to short muscle ratio is different, explaining their endurance? And further more, who cares?
They don't have genders, though if they did they would be closer to being males than not. Even the physically female Erinyes can and will fuck you and make little tieflings together.
Baatzu don't make babies, they harvest nupperibo.
I'm going to skip this chapter altogether since it dedicates hundreds of words to describing ""Colder Gellugons" (they shoot ice!) and balancing "assassin" variants of demons.