Hey, I remember this!
About the dragons: I agree with whoever said that thing about ...hold on, post finding.
Well, there are werewolves and vampires in Tolken, but they are more like giant wolves/man-bat things respectivly. Actually, they could make decent night creatures or semimegabeasts.
Also, on dragons: I proposed this in another Middle-earth thread, but one could use split up dragons into several monsters:
Cold Drakes were wingless and fireless, and could be stock creatures under the thrall of evil (naturaly, it would be increadably expensive for playable orcs to obtain one).
Fire-Drakes, or dragons that can simply breath fire, could be semimegabeasts. Really, there normal DF dragons, not much to change besides possibly a shrinking in size.
There's also dragons with both wings and fire, which are by far the rarest and are actualy exinct by the time of TLoTR. Presumably, they would be straight-up megabeasts that could presumably end a dwarven fortress...like Smaug.
Also, there are Long-Worms like Scatha, which, for the sake of expanding the creature list, could be Linnorm-like creatures who spawn occasinaly in colder biomes.
This is a good plan. Only we'd need to account for unique creatures like Ancalagon.