well, there are two broad classes:
the destructive ones. These would have similar roles to those of D&D orcs or hobgoblins. THey're out to kill and destroy humanity and their accomplishments
The subversive ones; these are less obvious. They're harder to identify on sight, and they try to persuade and subvert humans into destroying themselves. They're happy to do this to individuals, but if they can get whole societies to do it, that's even better.
None of them look exactly alike, though.
Statistically, then, you could group them. To put it in d20 terms, you could have stats blocks for each of small, medium, and large version of the violent ones (with some variation in each, to account for their abilities) and then add in a "special ability" like, some fly, some can tunnel, some are immune to something, whatever. And then do something simlar for the more subversive ones.
So yeah, there would definitely be a band of them living somewhere or wandering, like you'd have a band of gnolls or something in D&D.