You will need to activate all 4 corrupted engines around the map successfully (one in spawn, one in verrückt, one in Der Eisendrache and one in mob of the dead). Be sure to have gubblegums like double points, extra credit, shopping free on and besides, a few teammates to help opening up doors doesn't hurt either. You will have to open up a lot of doors, but don't waste cash on opening up doors you don't need to have opened. (you can either keep the area between spawn and origins or between spawn and shangri la closed for instance.
After successfully activating all of the corrupted engines, head over to the central area through one of the portals (Nacht der untoten). Over there, head upstairs to the room with Juggernog. The apothicon (large flying enemy will eventually fly past you). Once he does, you are able to interact with a little machine over on the side of the room. The 3 green lines will flash red and green. Now press
and you will catch the apothicon, allowing you to go downstairs over there and enter him, to go to the pack a punch room. (inside the apothicon). In the back area of this room, there is a large glowing parasite looking thing attached to the roof in 3 spots. Shoot all of these 3 spots and you are able to pack a punch.