SOLUTION COPIED FROM DRABIK!!!
You can obtain this achievement in Mission 3 of the Trouble With Clones DLC, 'Send in the Clones'.
As you progress through the mission, you will eventually reach an area where you are ambushed by loads of Brutes and Morningstar enemies. Run up to one of the Brutes and press RT for a super punch, defeating them in one hit, to unlock the achievement.
If for some reason you do not manage to unlock the achievement, you can simply replay the missions again after completing the DLC. To do this, save your game, and then reload it. Access the Missions menu on your Cell Phone for the option to replay the Trouble With Clones DLC again.