The Bureau: XCOM Declassified

This is a skill that your main character will acquire during his development towards Rank 10. Chosing that one will be automatic as there are no other upgrades for that level, therefore acquisition is unmissable.

I have gained it during my Easy playthrough, once doing all Minor Operations. Now with Commander difficulty I am focusing only on Major Operations and as I approach the end of the campaign, it can easily be the case that I'll not reach the needed level for it to unlock. Therefore, I suggest to do some Minor Ops as soon as possible, to make sure to unlock.

It will appear at the bottom of your command circle, at the same place where 'Heal' at the beginning. The cooldown period is very long, therefore you need to wait for it to refill and use it as frequently as possible, to make sure get enough kills until the end of campaign.

It is targetting as all other individual focuses ability: you select the victim and activate the ability on them. They will start killing their own, eventually unlocking the achievements. Lot of damage on the victim will unwear the effect, therefore try not to shoot at him as long as the effent is active. It is worthwhile to target sturdier subjects (Mutons), or effective killers (Phantoms), to make sure they can get some kills before their owns obliterate them.

The achievement will unlock during the operation, right after the 15th kill.

Basicly, the main goal is what Jissi said: Play every Minor Operations between Major Operations in order to reach Rank 8 as soon as possible. Normally you will able to unlock the ability in the middle of Chapter 5.

Here is what i did: In Chapter 5 there is an intensive last fight. I used Mind Control on elite Mutons every time after the aliens get off from the dropship. You will have at least 3 occasions to do this. (Because the Muton and the Alien soldiers are coming in the very same time, you have a pretty high chance to get some kills in this part of the game)

(One important thing which was already mentioned in the other solutions is that always make sure that the enemies are close enough to each other, to prevent idle enemies who does not attack their allies.)

The next Operation which can be very handful for this is a Minor Operation called Operation: Angel. This one gets available just right after Chapter 5. What i did here is to send back my teammates and used the ability on the Aliens. I did not use any forcepower, i just only killed the last remaining Alien on the field. So i hide behind the very first wooden plank on the map (where the first wave of enemies are patrolling) and waited them for killing each other. Don't panic if the plan doesn't work for the first time, just don't move and wait for recharge behind the cover. The aliens won't flank you, the rather just running up and down on the map, changing covers all the time.

Whenever you have no enemies left to use your ability, just move forward a bit to the corridor like part of the map and another 3-4 enemies will spawn and run toward you. When you can see them, immediately turn back and make a run to your previous cover. Make sure you beforehand destroyed the enemy landmines (they wont do anything with them, but you can never be sure enough) These guys are just regular Outsiders, so you don't even have to interrupt their fight and hurt one of them in order to get a kill (through the mind controlled enemy) Just after a few doors after this scene there is a medium size open area with a sniper, an Outsider and a Commander (Tech Commander i guess, i don't remember exactly) Make sure you kill the Sniper, because he can easily kill your mind controlled target. If you enter the area, an Elite Muton will arrive. Go back behind the glass covered corridor (where you can find some alien weapons) Order your teammates to stay there, and use Mind Control on the Elite Muton through the glass. He will take care about the 2 guys out there and none of them gonna actually come near you. The Muton will probably try to use some attack on you through the glass which will hurt you, so make sure you are using your Heal ability whenever you need.

This was the point when the achievement got unlocked for me. I hope it helped somehow. I know this achievement is hard because of the buggy AI, but it's not impossible. The key is the retreating and waiting.