Really Short Easter Egg, I cut in the beginning to when I turned on power since the stuff before it isn't important. This is a really easy easter egg for beginners!
Here's the steps to completing the easter egg:
Step 1: Turn on Power
Step 2: Build Pack-A-Punch
(Activate portal then go to either crash site or pond Depends on where it shows and use the teleporter to unlock the area with the part)
Step 3: Collect 3 Aetherscope pieces then craft it
(One piece is in yard near the stairs, another in crash site on top of an engine, last one is in the particle accelerator room near the bottom landing of the catwalk. After Collecting all 3 which spawn in a random order take them to the crafting bench in the Particle Accelerator room)
Step 4: Take Aetherscope to the medical bay then activate the portal and grab the book on the desk next to the computer. Afterwards talk to the 3 ghosts of the scientist.
(First scientist is in medical bay, the second near the reward stations, and the last at the bench to create the Aetherscope)
Step 5: Build the 4 elemental D.I.E variants
Fire: First step in getting the fire upgrade is to find the fuse box underneath the plane that life up in crash site when in the dark aether, the easiest way I've found to do this is to do it when crafting the Aetherscope, simple shoot open the box and collect the fuse. Afterwards take the fuse to weapons lab and while in the dark aether interact with the plasma cutter that is along the wall in the lower section of the room. You should be teleported out of the dark aether and can now go to the truck in pond, jump onto the bed of the truck and collect the fire variant from the box.
Nova-5: First go to the middle level of Nacht and outside of one the zombie spawns there will be a canister, right click with the die to vacuum it until it gets sucked onto your side of the barricade so that you can pick it. Next take the canister to the weapons lab and insert the canister into the machine, next kill a plague hound near the machine and allow the machine to vacuum up the cloud. Afterwards collect the canister and take it to the box in crash site and place it. After placing the canister you need to shoot it with any bullet gun to make it explode which will allow you to open the box and obtain the Nova-5 variant
Cryo: One of the easiest variants to collect is the cryo variant. To obtain the cryo variant you must have the D.I.E wonder weapon and use it shoot a box off the top of nacht. easiest way to do this is go to the nacht entrance from pond and look up. After shooting it with the D.I.E the box will fall and break exposing the beaker inside. Behind where you collect the beaker there is a tree with mushrooms on it, you need to get a Megaton to use his bile attacks on the tree/mushrooms until they glow. once they are glowing you will get an audio cue and then can place the beaker underneath the mushrooms. The beaker takes a little bit of time to fill so just keep an eye on it, after it is full take it to the medical bay and interact with the box to open it and allowing you to obtain the cryo variant.
Electric: Upon activating the aether portal in the particle accelerator room you must go around the map and right click with your D.I.E on 3 yellow glowing crystals until the D.I.E has completely become infused which will make the crystals stop glowing. These can only be completed one at a time. They are located in pond, outside of bunker entrance to plane crash, and on top of the roof of nacht. After infusing your D.I.E you must run back to the particle accelerator room and then shoot your D.I.E infused shot into the box in the corner of the lower part of the room. if done correctly one of the 3 lightbulbs should light up. Once all 3 crystals are used and the 3 lights are lit you can then obtain the electric variant.
Step 6: Shoot the 4 cylinders with its corresponding element type
Step 7: Collect Decontamination Agent
(Enter the portal outside of medical bay, next go to the catwalk in medical bay next to the collapsed section. An anomaly should appear that you need to talk to which will drop the aether wrench when finish. Afterwards go to yard and interact with the 3 broken spots on the tank, when done correctly a zombie will pop out of the top, when this happens throw an explosive into the tank. If done correctly the tank will fire. Afterwards go to crash site and pick up the decontamination agent and walk it back to the medical bay and insert it into the machine next to where the anomaly was. After doing that you need a megaton to spawn. when he spawns split him and take both of his halves under the chamber in med bay and they will be captured inside it. when both are captured activate the computer in med bay to decontaminate the megaton)
Step 8: Boss fight
(Activate portal in nacht then go to living room and interact with the anomaly and then with the picture to begin the boss fight)
Good luck :)