Ineti, you're just chocked full of good ideas! Something like this would be pretty useful, especially if organized as a quick-reference ready-to-go kind of thing. In fact, something like this sounds vastly more useful than the utterly worthless Fell Beasts book. I have found that in the official books the foes are, in general, too powerful for any reasonable "fellowship" against whom they might be pitted. I have had to "tone down" the basic Orcs and (especially) Uruks for my starting characters, using the listed book stats only for Goblins "champions" or Uruk-hai sergeants. And the drakes are so insanely powerful that only a platoon of heroes with 100 advancements apiece might be able to handle them. (Makes you wonder how Bard managed to beat Smaug?) So I would urge you to considering totally revising some of the book critters so that "stock" variants are actually manageable. I'm not saying that there should be a drake than any party of 4 starting characters could beat, but I would love to see some that are actually usable.
Also, I encourage you not to overlook something that is unforgivably absent in Fell Beasts: Unarmed Combat! After all, foes may every so often want to capture a character instead of mindlessly hacking away until death. (You know, like Goblins might want to grab some Dwarves and carry them off in sacks...)
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