Assassinating Mobile Units
If infiltrators can assassinate militia, why not allow them to be able to assassinate mobile units? This would be a bit more difficult to perform than militia (as militia are generally more relaxed/bored and easier to surprise than mobile men), and would be very important for a small realm trying to prevent takeovers. One could send an infiltrator or two to knock down the enemy's takeover unit to a more desireable number.
I think it would be pretty important, and am surprised it doesn't exist already.
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