Give us a bit more to go off of. What is the villain like?
Is he a particularly religious fellow? Perhaps his "seedlings" all bear holy symbols of that god (leading to some fun mistakes about the nature of the villain). Maybe they all quote sections of holy text favored by the villain ("My name is Legion, for we are many..."), or use an oath favored by the villain ("By the Vulture's blade").
Alternately, perhaps he himself has some kind of subtle insanity that is manifesting itself through his seedlings; heck, maybe he manifested Mind Seed as a self-defense mechanism, "shunting" the madness into others to spare himself its ravages (which, by strictest interpretation of Mind Seed doesn't work, but all that is necessary is that he *thinks* it does...). Perhaps his seedlings are all afflicted with his self-abusive tendencies (a trait of someone who feels out of control, and thus cuts himself to simulate some form of control in his life), leading them to cut up their bodies under their clothes, which could cause the PCs to leap to some interesting conclusions.
Or maybe he is from somewhere else, and all of his seedlings begin to speak with subtle hints of his accent. The villain might be remarkably superstitious, causing his seedlings to hunt out his preferred good luck charm and carry it with them at all times ("Hmmm...this is the third guy carrying a rabbit's foot on a silver chain. You think its some kind of cult or something?").
Also, check out p.150 in the DMG - there are some useful traits on Table 5-5.
Have fun!
. I find constantly gnawing on something crunchy, like sunflower seeds (or ice) is very obnoxious. Obviously there isn't ice in the game, but he could be always popping acorns into his mouth or something.
