String up one henchman and drop him to surprise a second (any play mode)
You can only earn this once you buy the skill upgrade ability to perform inverted takedowns (Black title with white eyes). Either enter a challenge or story mode, jump up to a gargoyle and hit to hang upside down. Once an enemy passes bellow you press to drop down and leave them hanging from the gargoyle.
Jump to another gargoyle by hitting the then select and aim your Batarang using the . Aim for the rope holding the enemy and press the to throw the Batarang and cut the rope to drop the enemy in front of the others.