I'd love to see lots of monsters in JADE. I think inspiration should be taken from Diablo, they are really dark and demonic like few. Can't think of alot of things that are not already in ADoM, though. Striders perhaps. More demons.
If there isn't already, I'd like to see a basilisk. I'm not talking about the serpent-kind, I'm talking about the large, six-legged, multi-horned beasts as they appear in D&D. I really need to check more about how the land in JADE looks like (random, duh) in order to tell which monsters would fit.