How to earn Power Chord achievement / trophy
For this I used Karnesis with Slam (Using Karnesis again on affected enemies violently hurls them down) and Flesh Bomb (Enemies affected by Karnesis land with a damaging blast). Set up your Loadout.
Go to Fristad Rock Morning, and work your way into Frank's Ramblin' Rock Club. Sneak or 'Rambo' your way in. You'll need to go in into the club without a ClassPass (or take it off once inside). You can sneak in the Club from below via the hole in the toilets from the watery area near the cliff club/bar.
Go to Frank's recording studio. Make him notice you and let the alarm go off, etc. Once he comes out simply keep using Karnesis on him until he dies. He will eventually die after a few attacks and the Achievement / Trophy will unlock.