Hidden within each Zombies map, you can find special hidden songs such as the Mad Hatter by Avenged Sevenfold. This that can be obtained by completing a series of tasks. Once you have successfully interacted with each particular object, a unique sound effect will occur. Once all items have been correctly obtained, the song will automatically begin playing.
In order to unlock the Mad Hatter Easter Egg song, you are going to be tasked with finding and shooting a series of small coins that are scattered across the map. The coins can be found in the following locations.
Coin #1: Danu Tower: Entrance – Located outside the playable map, the player can find the coin outside one of the zombie windows on the underside of the wooden staircase.
Coin #2: Ra Tower: Burial Chamber – Located in a corner near a burning fire brazier, you will find two chests. The coin is located in between these two chests.
Coin #3: Zeus Altar Room – Located on the side of the statue base, right next to a mystery box, you will find the coin.
Coin #4: Odin Tower: Entrance – Located inside of a metal grate, you will find the coin when you face the entrance to the Arena spawn area.
Much like the process used in IX, you will be required to find and shoot four different coins that are located across the map. The coins can be found in the following locations:
Coin #1: Forecastle – Located on the under right side of the stairs in Forecastle, the coin can be found on the back of a wooden crate.
Coin #2: Poop Deck – When facing the main ship, look towards the right side of the ship for a large roll of wire. The coin can be found between the wire and the wooden crate.
Coin #3: Lower Grand Staircase – Located on a broken wooden beam, you can find this particular coin when looking at the ceiling that is towards the stairs.
Coin #4: Sun Deck – Locate the final coin by looking on the Rescue boat that is filled with luggage.
This particular Easter Egg song is a little bit different compared to previous entries, as you will instead be required to input a series of numbers into the Citadel Tunnels in order to unlock the hidden song.
Step #1: Obtain the Warden’s Key, which can be found as a drop from the Brutus Zombie.
Step #2: Find and Ensemble the charged Spectral Shield.
Step #3: Take the Warden’s Key and charged Spectral Shield to the Citadel Tunnels, where you will find a locked cage at the bottom of the tunnels.
Step #4: Use the Spectral Shield to charge the numbers that are located on the cage. Interact with each of the tree numbers and import 1-1-5.
In order to activate the Shockwave Easter Egg song, you will need to find and interact with three green bottles that are scattered around the map. The bottles can be found at the following locations:
Bottle #1: War Room – Located in the lower level of the War Room, head towards the back-right corner and look underneath the terminal.
Bottle #2: Central Filing – Upon entering from the Side Passage door, head all the way to the back and you will find a bottle on the very top of the last row of filing cabinets.
Bottle #3: Porcine Research – Located in the back-left corner of the Porcine Research lab, you can find the bottle inside of an open cabinet.