This achievment is story related and cannot be missed.
*** Spoiler - click to reveal ***This is the final encounter with Scarecrow in the game. You will start to be affected by the the scare gas for a third time when you are back in intensive treatment. You pretty much know the drill by now. It's again a bit of hide & sneak followed by some casual fighting. All in all nothing spectacular. Still, I found it pretty annoying that the controls seemed a bit laggy in these parts of the game, which made nailing the timings unecessarily tricky. As soon as you are back in intensive treatment the achievement will unlock.
(video credit: Batmam Arkham Series videos)
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