Batman: Arkham Origins Blackgate - Deluxe Edition

This achievement is story-related and unmissable.

After the previous area with the electrified barriers, you’ll come to a chamber where Black Mask is waiting. The trick here is to stay in the darkness as Black Mask has two guns and can gun you down in seconds.

First, go into Detective Mode () to scan the area (floor grate, alarm, over-head lights). Once that’s done, hit the alarm at the far-right side of the room with your Batarang; Black Mask will go and investigate. Now, hit the over-head light closes to you with a Batarang and, as quickly as you can, get into the floor grate. Head towards the far-right floor grate. When Black Mask re-positions himself, jump out of the floor grate and hit the alarm on the far-left side of the room. As soon as you do this, jump right back into the floor grate and head to the middle floor grate to takedown Black Mask.

Note: While you're here, scan the clue right below Black Mask, The Bidding War case - Gold Coins.