In the same vein as the 3E Draconomicon is Lords of Madness: The Book of Aberrations (2005).

Old school D&D created lots of iconic monsters, but did so with, well, not a lot of thought toward making them plausible. Take the beholder, for instance. Cool as hell looking. Terrifying in terms of its powers. But…what the heck is it? Orcs or kobolds make a kind of sense – we have them in literature and their lives map to tribal cultures we understand from our own world. Beholders are something else. In 1E, it was basically the floating, murderous id of your dungeon master, existing to kill PCs.

Lords of Madness is an attempt to take some of the strangest monsters in D&D and make sense of them. Beholders are covered, along with mind flayers, aboleth, neogi, grell and the new-for-the-book tsochar. Each creature gets the Draconomicon treatment, breaking down their physiology, psychology, sociology, history and religious beliefs.

I’d say the results are mixed, but always interesting. The chapter on mind flayers is genius, through and through (they want to extinguish the sun!), with the grell and aboleth firm runners up – I mined a lot of this material in my long-running homebrew campaign. Neogi are interesting as are the tsochar – disturbing lamprey-like shapechangers the operated in the mode of Robert Heilein’s Puppet Masters – though they feel tonally different than the others in the book.

I still don’t get beholders, though. Love ‘em, and the book makes a valiant attempt, but nope, still don’t get them. If anything, attempts at explaining beholders make them even more bizarre. Did you know they make weapons that they can hold in their mouths? Yea. I am pretty happy that the artists didn’t try to draw that…