Earthfall: 20 Mins to Get 50 Kills

1) Invite a friend to help you.

2) Get the bridge down and climb over to the other side. Use the hand turret to disable bots (it’s just quicker).

Whoever needs the achievement, gets double pistols, his friend friend should carry maximum ammo, medkits, stimshots and grenades just in case (won’t really need them).

3) Wait for a Beast to spawn, then run back to the start of the map.
He cannot climb over the fence and will be stuck at it. Plus… none specials spawn either! 😉

a) he may spawn at the start of the map, in that case run a circle back to the roof hole, so he will follow you and eventually arrive at the stuck point.
b) Blackout may spawn. This thing will not get stuck, so make sure your friend kills it.

4) Got the Beast stuck? Friend armed and ready? Head to the container, jump on it and do the kills.

Your friend runs around killing green spitters, lures new aliens in
(they switch interest to the player on the container) and kills over-crowed species.

They literally jump to your hands! :3
Ignore Beast’s roaring. 50 kills done in 20 mins or less 😉

P.S. so far this strategy worked on me (Lord of War) and zep.