How do I scare the pants off some henchmen?

Solution 1:

I just got this one last night. I was almost about to ask a question myself before I figured it out. The answer is two-fold:

  1. They have to be terrified. If you point to them in Detective Vision and you'll see their current state. You can only scare thugs who are in the "terrified" state. You can increase their terror level by taking out thugs without being spotted. They'll start yelling things like "we're all gonna die" and "forget you, it's every man for himself!" when they're getting scared. I've also read that cutting someone down who is hanging from a vantage point while other thugs are nearby will cause them to become terrified.
  2. You have to appear suddenly. When in the "terrified" state, thugs will randomly switch direction to check and see if you're behind them. Sneak up behind them, and be there when they check for you :) Other people reported (in that same forum thread) that you can do other things besides sneak up behind them, ie jump out of a grate or glide down in front of him, for instance.

Solution 2:

In the game you always need to stay hidden, (like in a air vent or something) and when the moments right you take one guy out and the others will eventually find out and will get even more scared. Try to take them out silently one-by-one, if you make noise it will make them suspect it is you. Its also affective if you hang them upside down from a gargoyle, then when they are all there, make sure your currently outside of sighting range and throw a batarang at the rope (not the guy) make sure that they start yelling out things like "we're all dead!" etc.