Well The Easter egg is pretty simple, Follow the Guide (In the score board menu),

My tips for this map:
1- At the start of the map before you activate the elevator, pick up the adrenaline and the Bowie-knife.

2- Activate the elevator however stand just a bit in front of the elevator not too far just where the zombie spawns from the roof/floor (forgot which one) this will allow you to one shot the zombies with the pistol you spawn with and knife the zombie which will spawn in front of you before it is able to attack you

3- Once you completed the little lock down step mantle over the wall and go grab the gun from the room, I would prefer the m4 as it is my go-to weapon on this map (Enough bullets, 1 shot headshot, and fast reload). Once you grab the gun, get ready to activate the alarm. USE nightmare mode for this as It's so much easier to get past the zombies, once you activate the alarm get into nightmare and see the first letter above the box you just activate, go out into the hall where the elevator is and run right one letter should be on the wall just outside the place you just mantled from, and the last one should be at the other end of the hall in the barrier. (follow the arrows)

4- Once down in the elevator, rush into the left hall then quickly run into the office and pick up the fuse which is based in one of the 4 little draws on the desk. Then run back to the main lobby and fight off the zombies. IF YOU GET LOW QUICKLY HOP INTO NIGHTMARE MODE TO GET RID OF THE ZOMBIES (you will not regain hp in nightmare mode so be careful when coming out of it make sure the zombies are far from you)

5- Keep following the guides as it pretty much tells you what to do.

6- Unlock security room by finding the little ripped paper around the map. It's easy to find, just hug the walls in most rooms, and you will find it in 5-10 minutes of searching.

7- Security room monitors are easy, look round the map for TV's you will hear static around the map when you are near one (they're on the roof in corners). The TV's have numbers under them telling you which position the little symbol will be in the security room monitor.

Bonus Fact- When activating the security monitors when putting in the symbols all doors will open and no more lock-downs will occur, ALSO the Lab will open. This is where you will build T.e.d.d

8- T.e.d.d Is pretty weird i spent 40 minutes looking for the key card however it drops of the scientist when you kill it with the RC-XD

9- T.e.d.d's Head is in the lobby behind the counter, just interact with t.e.d.d, and you will get the head.

10- Go to scientist room and place the head on the bed and activate it by the Ascension panel in the corner near the steel containment tubes.

11- The rest of the EE is pretty simple, go to the chapel for the kronorium.

12- Before you activate the kronorium make sure you have a Molotov. Throw it down by the entrance of the kronorium altar and stand back, and the zombies will die. I would advise you to have a flamethrower which is based in the security room.

Bonus Tip- I would get a LMG from one of the bags.

13- Go place the done kronorium in the room just above the main stairs, go through and your going to be ready for the boss fight.

14- When your in the boss fight grab Adrenalin this will be your best friend. Use Adrenalin and spray your LMG at the Nightmare boss and use your flamethrower. This way worked for me

Anyways this is how i beat it every time

Any questions just leave them here