Difficulty: Extreme (or higher.)
Faction: Automations
Mission: "Reduce enemy numbers"
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Recommend bringing a Railgun for this achievement, though can be done with other powerful support weapons. On this difficulty or higher there will be a few Hulks spawning, shoot the arms of the Hulk with the rail gun. May take 1-2 shots on the arm to destroy it, you'll have to do it to both arms.
Avoid killing the arm-less Hulk and proceed to killing the other other Robots until the mission is complete. Extract and the achievement will pop. (as long as you extract alive and the Hulk is also alive.)
Note: If your teammates extract and you don't? They will get the achievement and you wont.