Dead Effect 2

Mission 18 Brain draining
This was easily the most annoying achievement
You will want a few ammo packs just incase, now as the achievement states you cannot take a total of 10% damage. It doesn't mean you cannot go below 90%,
Now for the mission walk upto and stand infront of the 1st door once it opens, shoot a bullet to alert all enemys in the room, they will all run at you, just keep shooting. If they start getting close to you just move down the stairs. They will not follow you, the music will stop once they're all dead. Now do the mission requirements until you're asked to mess around with controls, once you get close to pannel 1, a chainsaw zombie will spawn, keep your distance keep moving if required nothing else will spawn at this point. Once he's dead move to the 2nd pannel a fat spitting zombie will spawn. Same deal from a distance, grenaides etc. Once he dies the acid zombie will spawn (on the same location), same thing. Now do not walk over the acid on the floor just wait it out. It will vanish in 30 secs. Now for the fun part. The drone will wake up. You want to be up the top and hugging the generator next to minikin, the drone should get stuck he can still hit you tho so be careful, you want to get atleast 3/8ths of one of his sides visible, then just lay into him and dont move unless he does. Most of your shots will hit walls and clippings instead of him, but if you see his health going doqn you've got a good spot. I hope this helps. This is how i unlocked it, possible video will be considered to show how I've written it

I've included a video on how to do it. just need the skill Gigashot to do it as i've done in the video. or if you don't have a shotgun and Gigashot, refer to what i written above. if you don't have a decent weapon. the shotgun i was using was a level 18 full upgraded purple.