Monsters

Planescape isn't really "about" monsters. One may think of the classic AD&D campaign as travelling into some wilderness or subterranian labarynth, slaying terrible monsters, and running off with their treasure. Surely, one can do this across the planes, but it's not the main focus of the campaign. As such, I find that I don't use the monsters books all that much.

However, combat will arise; there are lots of testy people out there, and any cutter who wants to guard something or go after somebody else is liable to send some of the monsters found in these books to do their bidding. What's more, these books can be thought of as books of races and NPCs, not just as books of foes. Indeed, there are sects (similar to factions, only not based in Sigil) detailed in these books, as well as other creatures with whom characters are most likely to interact in ways other than combat. The planes should be weird; Primes who get to Sigil should see all kinds of things walking around that they aren't used to seeing just walking around. These books provide a lot of source material for that.

In addition to the books below, the core boxed set and each of the "Planes Of..." boxed sets include a monstrous supplement. Your favorite source for AD&D monsters is also useful.

A Guide to the Astral Plane has an extensive chapter all about the Githyanki (who currently use the Astral as their home plane.)

• Planescape Monstrous Compendium Appendix I
• Planescape Monstrous Compendium Appendix II
• Planescape Monstrous Compendium Appendix II
• Faces of Evil: The Fiends

Faces of Evil: The Fiends

A 96-page book all about fiends, with almost no game statistics at all. This is not the book that will give you the fiends' hit dice, armor class, detailed spell-like abilities, and so forth; for that, you need to refer to the various Plaenscape Monstrous Compendiae. Rather, this is an in-character book written by residents of Sigil with the chant and the dark about fiends. There are major chapters about Baatezu, Tanar'ri, and Yugoloths, plus an additional chapter to clean up the Gehereleths and other not-quite-fiends (such as Night Hags and the like). Each chapter has a (fictional) editor and three (fictional) writers, each of which write in their own voice.

This book is great. If you're thinking about running a campaign that focuses on or even touches on the Blood War or other machinations of fiends, this book is highly recommended. Especially for myself, as one who plays Planescape using something other than D&D rules, there is basically no "wasted" space in here. The in-character writing is usually unobtrusive, if that sort of thing bothers you. If it doesn't, you will notice the differences in how the fiends are presented, thereby rendering everything in the book perhaps a bit suspect. While this might sound annoying to the GM looking for the straight dark of things, it does give you the option to slightly modify fiends from what the book says while remaining consistent with the book! Where the in-character writing is not unobtrusive, it is often amusing; in particular, the Slaad Xanost (from Uncaged: Faces of Sigil) has some quite entertaining prose when he is unable to restrain himself.