Two Heads, One Bullet

This can be done anytime in the game, but is quite tricky to get. We recommend carrying a decent sniper rifle, with the highest damage per shot you can get, throughout the game until you unlock this.

Ideally you want two or more enemies in a group that haven't spotted you yet - where you can get a good angle on them for a headshot on the closest and then into the head or body of the person behind.

It won't always happen, even when it looks like it should - and you tend to only get one chance per group of enemies as they'll become alerted and start moving around after the first shot.

Pick lower level/regular enemies as they are easier to kill. Also consider dropping the difficulty for this achievement to have a better chance of killing (vs only wounding) both the enemies.