Livelock
50 Achievements
1,000
15-20h
Terminated
Destroy 100 Upgraded enemies
25
6.01%
How to unlock the Terminated achievement in Livelock - Definitive Guide
Edit: It did, however, pop on my first replayed mission while hunting for the audio logs I missed. Perhaps there are more upgraded enemies on higher difficulty settings.
Upgraded enemies can be identified by the same name located above their health bar but also by the blue/purple/yellow shield they spawn with. Most levels will have one if not more of these guys to kill but Act 1-7: Limited Edition has a lot for you to farm.
From the starting area, head up to the first objective where you need you need to destroy 1/6 Abandoned Fabrication Module and you'll come across your first 2 Upgraded enemies. From this centre area, head left and up the wooden slope. You'll now be confronted by at least another 7 Upgraded enemies. Once they've been dealt with, keep heading forward, down the other side and turn right for one more. When they're dead, just restart the mission and repeat.