This achievement just popped for me, so I'll add my 2 cents. I tried a few runthroughs of village attack, but it didn't seem to give me anything. I've just spent about 10 minutes on 2-1 in the first bit; threw my grenades at the flying guys, killed myself, repeat. It popped after maybe 7-10 attempts. I found it's best to wait for them to land and then take off again before throwing, because sometimes they hover or jump towards your general area (they take off as you approach the ruins).
I tried the magneton trick mentioned above, no love.