- gamertag: Krynin
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Just play through the entire campaign from the start without killing a single Engineer. They will blow up when their squad dies, but as long as you didn't actually hit them with anything, it doesn't count as a kill so you are still safe. Just be careful not to shoot any of them, especially on the level where you get in a Banshee and have to escort the hijacked Phantom; some of them fly around in that level and you can accidentally hit one, ruining the achievement.