Easter Egg Steps:

1. Do the tasks listed in the note located at spawn.

2.

Fill Soulboxes

Locations:
-Furnace Room
-Outside in front of jugg
-Between two shower rooms
-Beneath the swimming pool, under a pool of blood (unlocked by finding all the shootables)

Shootables
(Most of them are highlighted by a BLUE spotlight)
Locations:
-Inside a zombie barricade underneath a ladder you had to climb
-directly above a box location, inside the window of a building (highlighted by blue light)
-rooftop (look far away, highlighted by a blue light)
-Outside of swimming pool, ontop of a mansion (above Speed Cola).
-Swimming pool place, corner, beside shield piece (blue light).
-Second floor balcony in one of the hallways after you teleport
-In a bathtub at one of the hallways after you teleport (also have a weapon part HINT)
-Temp room before you reach Pack a Punch (second floor)

Encounters with Lisa
-ANS: 2

FK9 Weapon
Wallbuy weapon for 1500, looks like a Cordite
Remember the number written on it's Magazine

Find the babies

Locations:
-Roof Top
-Platform/Scaffold
-ground in front of window

You will hear a laugh when all babies are found

Floor
After you teleport to the hallways
Look for the floor number that is written in RED.

If you see a slightly opened door, look through the opening at the sink. To unlock the door to proceed to the next hallway.


After the soulbox underneath the bloody pool is filled:
You can enter the toilet that require souls to open.
Inside you will find a room where you can enter numbers into 6 dials.

CODE:
1st Dial: Number of Lisa encounters : 2
2nd Dial: Number on FK9 wallbuy: 0
3rd Dial: Number of Soulboxes: 4
4th Dial: Number of SHootables: 8
5th Dial: Number of Red Letter Floor: 6
6th Dial: Number of Babies Found: 3



After you can go to a terminal in the same room to Confirm the code. Then walkthrough the fire. You can prepare a bit there, pack a punch, buy some weapons, do whatever.
Once you get out, you can now return to town and start the attackables (the cages you seen before). After finishing BOTH attackables the Lab 935 Gate (Big gate, also a shield piece location) will open and you can resurrect Brutus and start the final fight.

Then go back to spawn and rest is self explanatory.