Kill three guards simultaneously with only throwing knives. (20 G)

There are many places where there are multiple guards to kill. You want to find guards that don't have any armor on or very little (that way they die in one hit). All 3 guards have to die in one hit. Go to an area with at least 3 of the above guards and make sure you have knives equipped. Hold RB to select them on the right stick's wheel. Hold down Y when you have them equipped and you should see the guards light up. Now let go to kill them. If you have a bad position, you may press B to cancel the throw and try a different angle.

If you still have not obtained the achievement by Sequence 4 Memory 1, then you can do it within the memory. Get to where you have 6/9 people knocked out and you'll come into an area with a ton of enemies. There are a good amount of unarmored ones.