Difficulty: Any
Mission: Countdown
At the beginning of the mission, you'll be dropped off via helicopter on a skyscraper. You will then grapple down the side of the building with Captain Price. You can actually grapple down in two fashions, right site up or upside down. I recommend staying upside down.
You'll be warned of hostages that need to be freed and this is where the achievement will begin. There are just 3 levels of hostages to clear out and you will complete them one by one.
First Level: 2 enemies
- Upon grappling down to the first level, you'll see the two enemies standing close to one another. I'd recommend getting into position where you can line them and take two quick shots.
Second Level: 4 enemies
- You'll have two enemies on the far left and two right in front of you. I recommend walking over to the two on the left and quickly taking them out. This should not alert the ones on the right. I would then shoot the one CLOSEST to you first, followed by the guy in the back.
Third Level: 5 enemies
- This one took me a couple times. You'll see 1 guy on the far left by himself, two on the far right that are standing, and two enemies that walk up the middle . I would recommend taking out the two guys on the far right, and then sweeping to the left with the middle and then far guy on the right. May have to alternate between the middle and the guy on the far left.
Should you have any issues, you can always revert to the previous checkpoint and try again.
Here is a video from Maka91Productions on YouTube: