If you wanted to spell out all the special types of stealth units that you would want to prevent from entering your territory with a NAP what would they be? So far, I can think of:
Preacher or Heretic units
Assassination
Seduction or Corruption units. (Corruption is like seduction, but i think only 1 unit has it.)
Stone Idols
Bane Venom Charms
Rlyeh sneaking Void Spectres.
Spies causing unrest.
Pan/Bogarus units causing unrest.
Feeblemind/Misfortune from artifacts.
Have I missed anything?
Thanks vfb.
I have added your ideas into one copy-paste-able list.