Locate the "Dragon Command" control room that contains the incubator machine and the many green monitors. This is inside the colosseum building with the star on the front and the giant pillars outside. Flick the power switch on - it's located at ground level just beside the machine itself.
Once the power is on, kill zombies to collect "Code Cylinders". Insert these cylinders into each of the three consoles: Red, Yellow and Blue and defend the pods for around 30 seconds to claim a Network Circuit.
Repeat the process until you have all three Network Circuits and then insert them into the machine inside the "Operations Bunker".
Climb onto the upper platform inside "Dragon Command" (near the blue console). Wait for a dragon to arrive then board by jumping on to his back. Wait a second for the animation to start at which point you fly out of the main area and are dropped into a bunker location.
This bunker appears to be a dead end but it's just like the Golden Gate Bridge from Mob of the Dead. Head downstairs to the Pack-a-Punch and use this time wisely to upgrade your weapon.
While you're inside the PaP room, go upstairs and get the crystal to claim the Dragon Strike weapon. The bunker will lockdown so be prepared for a fight while you defend yourself against the oncoming horde and Russian Manglers. Do this step when you are ready because this lockdown is hard.
Once the lockdown is over, head down to the sewer entrance (the one which takes you back to the main area of the map) and stand in front of it. Look up and slightly left - see the dragon egg there? Shoot it to make it roll off, then pick it up. The Dragon Egg should appear in your inventory.
Stay within the PaP building and wait for the Valkyrie drones to appear. Stand close to the generator which is near to the sewer entrance - it has a green cover on top and a green/red control panel on the left side.
Simply kill a drone near the generator to complete this step. The generator should spark and start to hum to signify that you've done this step correctly. If it doesn't spark, press square to get things started (or to restart the generator at a later time).
Take the sewer back to the main area.
Next, find the Valve machines which look like a set of tubes with the numbers 1, 2 and 3 on the front. There are several of these around the map.
Interact with the machine to rotate the dial so that it points at a particular number. Each time you change the number of a particular dial you are re-directing the pressure in the tube, which in turn affects the next tube in the sequence. The goal is to choose the right sequence of numbers to allow air to flow through all of the tubes, pushing the Cylinder out the other end.
Originally, this was an incredibly difficult step in the Easter Egg but the instructions below will help you solve it in a couple of minutes:
Successfully releasing the pressure in the correct order will push the Cylinder along the pipes and onto it's final destination. When all of the machines are correct, a new Cylinder will drop out of the final machine.
Take the cylinder and place it inside the Sophia machine in Dragon Command.
Take the newly acquired dragon egg to a dragons nest which can be found in the spawn area or outside of the Dragon Command entrance. Place the egg in the nest and wait for a dragon to breath fire on the area.
After the egg cools, go back to spawn and check your tombstone for new challenges. There are three that you must complete:
Complete all of these before moving on.
Take the dragon egg to the PaP room and place it in the cylinders under the bunker. Kill zombies in the vicinity to charge the egg, you should see lightning spark from the zombies as they die. After enough kills, try and pick up the egg - you should see a message which says "the egg must cooldown first".
Complete another round to let the cooldown complete and then pick up the egg. Take the sewer back to the spawn area.
The Gauntlet of Siegfried is the new Wonder Weapon for Gorod Krovi and you'll need this weapon to send the Power Core to Nikolai's location.
Now that you have the dragon egg, simply interact with the challenges tombstone to claim the Gauntlet of Siegfried.
The next step of the Easter Egg is to collect 6 trophies/statues that are found in different areas of the map. Some are in plain sight whilst others are revealed by interacting with certain objects.
Once collected, each of the trophies appears underneath the large monitor on the opposite side of the room to Sophia. Trophy locations:
Go back to the Sophia machine and take note of the cylinder panel on the left which displays a series of letters. Press square to start the password phase. Now shoot the individual letters to spin each section of the cylinder, eventually lining up a series of letters to form the password.
The correct password is KRONOS. When you're ready, press square to "confirm the password".
For the next part of the Easter Egg you will need to complete 6 challenge style trials for Sophia. The first five are presented in random order but the sixth is always the same. To start a trial simply press the green button underneath the large monitor opposite Sophia. Here are all six challenges:
Sophia will say two minutes remaining and you now need to sprint, find the bombs and defuse them. There's a bomb in each section e.g. Tank Factory, Supply Depot etc. Check the 935 control panels on the walls to see which device is the bomb.
The order in which you need to defuse the bombs is presented on the large computer monitor. Watch very carefully for the sequence.
If you successfully defuse the bombs in the right order Sophia will say "self destruct sequence stopped, thankyou for preventing our extermination". Remember, if you can't defuse all the bombs in time, stay away from the bomb sections to stay alive by either going to spawn or by riding the dragon.
A yellow spark/orb will appear somewhere on the map. Continuously shoot the orb so it moves and eventually disappears, before reappearing in a different location. Repeat the process many times and wait for Gersh to finish speaking before following his location each time.
At this point in the game there will be infinite zombies until the orb completely disappears so it's a good idea to use Gobble Gums to slow zombies down.
If done successfully Sophia will say "beginning information extraction" before Gersh screams.
This time she wants you to escort a Russian Mangler back to the teleporter in Dragon Command. Be extra careful not to kill the Mangler as you tempt him back to Sophia.
It's hard to distinguish the Mangler from the many zombies which will be coming at you by this stage, but listen out for him and watch for his green eyes and slow movement which is a giveaway sign.
Similar to the Mangler trial, simply escort the Valkyrie back to the teleporter in Dragon Command without killing it. Again the "friendly" Valkyrie has green lights.
Defend a pod which drops outside the map. Once secured, send over the Whelp (little Gauntlet dragon) to pick up the cargo and bring it back to Sophia.
Obtain the key card from the large monitor opposite Sophia and go to the hatchery (in PaP where you incubated the egg). Insert the card into the computer with red lights and defend the area from Manglers. Once done, return the card to Sophia.
Pull the Power Core out of the right side of Sophia. Dash to spawn, face Nikolai and use the Gauntlet of Siegfried to let the little dragon fella fly off and deliver the Power Core.
Make sure you have all the Gobble Gums, ammo and perks you need before attempting this step of the EE.
Have all players stand on top of the sewer gate (with the red Russian star) in front of Sophia. The gate will open, dropping players down into a new sewer section, eventually throwing them out into a new open area. This is the final BOSS location.
Nikolai 1.0's mech is in a standoff against the mother dragon. Fight along side him to kill this giant beast while you try and survive against the near impossible swarm of zombies and fire that plagues the area.
After defeating the dragon, Nikolai will turn on you instead. Sprint round the perimeter of the arena, avoiding his attacks by using the corner trench sections. Aim for Nikolai's weak yellow spots to take him down.
After killing Nikolai, you have completed the Easter Egg and the cutscene will now play.