Power - Buy your way into the underground room. Now open up the door that leads to the power and turn it on. Now interact with the two computers that are marked on each side of the particle accelerator. Now go to the pack-a-punch machine and go into the Dark Aether. Go up onto the main land and to the tunnel that is marked on your screen. Go through the tunnel and pick up the pack-a-punch part, then run to the pack-a-punch machine and forge it.
Keycard - Once a Megaton spawns, kill it and the two zombies it splits into. Once done it should drop a keycard on the floor which you will have to pick up. Now go to the Weapons Lab which is one of the two hallways to the particle accelerator room and go to the box spawn. Now across from the box spawn there should be an area that it says you can place the key card.
Remote - Pick up the remote that comes from the place you put the keycard into. Now go to the Nacht Der Untoten area called Living Room and place the remote in the window across from the stairs. Now get a hoard of zombies and kill them all in front of that window. Once you have that interact with the remote and get around 30 kills next to it. Once done, interact with it again and a door next to the window should open. There will now be a D.I.E Shockwave on the ground to pick up.