To perform a melee attack in Andromeda press the
For a more powerful melee attack jump with the
button and then press
you will get an area effect that is quite devastating.
I have about 90 kills after just a few hours of multiplayer APEX missions. I also pushed up my melee damage with one of my skill points and can kill almost any red bar enemy if they are half dead with one airborne melee.
And just for clarity this achievement will be very quick in the multiplayer part of the game.