twisted thought...
Check Dopplegangers by Goodman Games...
Mimics are older dopplegangers! They tend to be look outs and teachers. The ones you meet in the dugeon are ... well, let's just say that the environment has a telling effect.
Older still are dopplegengers that pretend to be buildings!
Given time...everypart of a town (streets, benches, houses) are mind reading dopplegangers! Combine that with a hive mind and the ability to "record" their memories into a memory pool, as well as share those memories with others, and you have antagonists that never die (unless you take out the nest).
Scary thought #2: IMC, I use both this example of the Doppleganger and FR's Greater Dopplegangers. The second eats normal minds, adding even more to the Memory pools (MWHAHAHAHAHAHAHAHAHAHA!!!!!!!!!)