Death From Above is unlocked very late into the gameA Death From Above kill is achieved by holding
whilst in the air which brings up a reticule on the floor to aim using the
you can them press
and your character will dive into the ground damaging anything below it.
There are a few ways to grind this out but im going to assume that you have completed the story for the bulk of my solution but it is worth mentioning that there is apparently an exploit of sorts for the final mission where...
*** Spoiler - click to reveal ***Once you are fighting robot Zynyak and he jumps into the centre shield and begins throwing C.I.Ds at you that at this time if you throw a few C.I.Ds back he will begin spawning infinite amounts of aliens, however for me they were death bots instead which do not count.
Firstly you'll want to find a Hard difficulty Super Powered Fightclub activity, there is one in the centre of the map (Shown in the video) start the activity and complete the first wave.
Now you'll start the second wave which is King Of The Hill,
ignore the hill and instead stand on an open flat area. Several menu with bats will continuously come for you and agro to you now which is perfect as these still count as aliens. Jump in the air
and hold
now if you havnt already equip your freeze blast
and wait until there are 5-7 enemies and blast them with your freeze blast
then whilst they are froze press
to perform a Death From Above attack. The kills will come up as shatter kills for the freeze blast BUT they will count for your Death From Above kills.
You have plenty of time on the counter to get all 100 but if you happen to fail make sure you
EXIT the activity to start over else your kills will not count for your challenges.
Here's a video.