Since I haven't seen a text guide for this anywhere, I'm going to post one from what I've been able to discern from the various other videos that have been posted.

• 30 Melee kills
  
• 40 Grenade kills
  
• 50 Headshot kills
  
• 60 kills

There are now four meteors around the map that must be filled with souls

Locations:

• In the cave next to the grenade wallbuy
  
• Next to the MP5 wallbuy
  
• Across from the truck near the Ranger wallbuy
  
• Across from the Ballista wallbuy

When this is done, the Shovel and Thundergun power-ups (same mechanics as the Call of the Dead Wunderwaffe powerup) are now obtainable in spawn

• Shoot circle with lightning bolt in it with Ballista (?) to unlock power (found on the opposite end of the map on wall opposite Ballista, near lamppost)
  
• Use shovel and dig up a pile of rocks for the power switch (found next to root in the corner of the map by the crashed plane)
  
• Build the power switch on the panel
  
• Perks can now be bought from the arcade machine (starting limit of 4, additional slots can be purchased for 4000 each)

• (Red) In spawn on the ledge above the Pack-a-Punch alcove entrance
  
• (Green) On a tree outside the window by the
  
• (Violet) On the brick/rock wall three bricks to the left of the violet skull
  
• (Yellow) On the ground outside the map near the base of the Pack-a-Punch building in the last ridge
  
• (Blue) In a crevice on the roof on the opposite side of the cave from the grenade wallbuy (blends in really well)
  
• (Purple) On the tree branch between the cave and the crashed plane
  
• (Orange) Inside the shack with the crashed plane, just to the right of where the second beam meets the left-side wall (easier to see when crouched or prone)

Each chalk that's shot will also spawn in some symbols by the skull with the same eye color; not quite sure the significance of it

• With the bottom symbol being 1, and the top being 7: 1-3-5-6-7-2-4
  
• This will unlock Pack-a-Punch

Now that Pack-a-Punch is unlocked, there is a button that can be interacted (the type that are interacted with to start the eclipse in Shangri-la) with to start a timed step
There are four other buttons around the map that must be shot in a certain amount of time

Locations:

• On the left outer wall of the "building" to the left of the Pack-a-Punch building
  
• Next to the waterfall behind the power building
  
• At the very top of the Pack-a-Punch building
  
• Ground level on the side of the cliff between the cave and the airplane (just behind the bushes)

Once done correctly, a noise will be heard

• Three Napalms must be blown up by the green meteor in spawn
  
• Once completed, the boss fight can be started for 30,000

• You will need guns with heavy firepower (PPSh and Ray Gun MkII work very well)
  
• The boss fight will start, locking the player in spawn with a shrieker with a health bar
  
• Originally there will be no other enemies, but eventually wolves and zombies will begin to spawn in
  
• As the boss fight progresses, the next areas on either side will open up
  
• If playing solo, it is more than likely that you will need a Max Ammo to finish the fight, so try and manage your drop cycle to get one in the boss fight
  
• Once you have killed the boss, a cutscene will start and the game will end

Each two perk bottles shot that are the same bottle with give a free perk. These can be done at any point in the game.

Juggernog:

• On top of the waterfall (easiest seen from the chain-link gate in front of the plane)
  
• Sticking out of the top of the tree stump to the right of the green chalk location (just the neck sticking out, very hard to see with anything but a sniper)

Speed Cola:

• In the rock pile near the plane behind the left-most closest small rock
  
• On the right-most branch of the tree near the first listed button in Step 6; close to the trunk

Unsure what exactly these do, but I believe the symbols associated with each are supposed to form some sort of order. These symbols show up as the chalk of the respective color are shot.

Locations and Symbols:

• (Red) In spawn near the B23R, has a single horizontal line
  
• (Green) In three tree near the Ballista; has a peace sign that could mean 2
  
• (Violet) Near the Ballista; has a funky symbol and a key with an 'X'
  
• (Yellow) On the rock by the Ranger; has a diamond
  
• (Blue) In the cave; has Roman numerals 'VI' which translates to 6
  
• (Purple) On a log outside the cave; has two lines that meet at the top left of each and a key with a 'P'
  
• (Orange) In the canoe near the plane; has Morse code that translates to 3

Again, unsure what these do (likely some sort of code that must be deciphered), but they show up after various chalks are shot. A crate in the hut with the orange chalk can also be blown open, revealing a chalkboard that is likely connected to this

Locations:

• Just to the left and above the Ballista (after the green chalk is shot)
  
• On top of the power building (after the red chalk is shot)
  
• On the rock wall behind the Mystery Box and grenade wallbuy (after orange/all chalk? are shot)
  
• On the face of the rock cliff directly behind where the diamond for the yellow chalk shows up (unsure when)

The pieces, when assembled, form the following matrix of letters:

X N K B W H W H E T E U U I W U I U E E N K

L E H U O Q U R Y Y F R T V H D X B M V R U

P O F F T E D T E D W O H F E U S O B S E B