Rise of Nightmares

The achievement description after you unlock it changes to kill 100 enemies with power weapons. This includes the chainsaws, the drill and my personal favorite, the meat mincer. Easiest way I found to obtain it was the first scene of act 4. After you take the dog to his body and he asks you to go find his heart you have to climb a ladder. Instead of going right to the lever, first go around the corner to your left. At the end of this path there is a breakable crate with the meat mincer in it. Then you can go pull the lever and suddenly you get assaulted by enemies. Kill everyone up top with you, then everyone in the blood. After you go outside you can kill a few more enemies just avoid killing the zombie carrying the heart you need for your objective. Let him kill you and you will start right after you pulled the lever still holding your mincer. You can get about 20 kills in five minutes with this method, so it will not take very long to get the achievement to pop.