1) City Guards have Detect Hidden and Forensics skill. Why? I have no idea.
2) Town Criers are equally strong as city guards. They would whoop your behind if you were ever able to engage them.
3) Daemons have a wide-ranging AR - nearly every npc has a static AR, but daemons spawn between 3 and 18.
4) Air Elementals and Fire Elementals are fast as heck - like 150+ dexterity.
5) Ogres hit hard - harder than drakes, harder than almost any other critter.
6) the code rates monsters in difficulty on a scale of 1 to 11. The 11's are: balron, ancient wyrm, and poison elemental.
7) dragons and ancient wyrms have the same HP range - 700-1100 and the same AR. Defensively, they are almost identical; the ancient wyrms have a slightly higher wrestling skill.

9) drakes used to require GM skill to tame; dragons were 99.
10) summoned daemons hit harder than dragons, but of course don't have firebreath.
11) poison elementals had the strongest AR in the game and the 6th highest HP
12) dire wolves and hell hounds were identical twins, statistically, except for the firebreathing
13) reapers could only cast up to second level spells; a bunch of monsters could cast up through level 8. Though this is just a numerical cap. I'm still working on getting the code for the actual spellcasting AI.
The abyss shard statistics are largely accurate (http://web.archive.org/web/199910130013 ... index.html). For AR, they are identical to the demo. Some of the values for STR are higher than the demo, but it's a real good reference point.
Anyways, I'll add to this as I discover more fun facts and info.