Boost jump, dash forward, then air stomp on an enemy.

You need to have the assault exo for this trophy, an example of a mission where you have that would be the very first one. What you want to do is:

Jump ( [ Register or Signin to view external links. ] ), Jump in the air ( [ Register or Signin to view external links. ] ), Air Dash forward (Click the gold [ Register or Signin to view external links. ] , move it forward), then stomp ( [ Register or Signin to view external links. ] )

If you do that near an enemy, you will stomp them from the air and kill them instantly. It might sound a little tricky to pull off but it really isn't. Remember that this can only be done with the assault exo. The specialist exo cannot double jump therefore you cannot get it in the missions where you use that exo suit. For a visual walkthrough, refer to the video below: