Corruption

Corruption is the major easter egg for the Zombies map Sorrow. It focuses on Edward Richtofen and the Celebrity Group collaborating on something undetermined. It spans 8 steps. The reward for completing the easter egg is seen below.

The transcript is seen here.

Step 1
We Meet Again

Step 1 is completed by killing a Camper Zombie and obtaining the Random Perk Bottle from it. Richtofen will say his usual line, to which the characters say that they recognise. Richtofen will then say that he needs their help once, which they agree to do due to the reward they got last time.

Step 2
The Map

Step 2 begins with Richtofen asking them to find a map of the village. The map is located in the hut with one door and no roof at the end of the village. Once it is obtained, Richtofen will thank the person who obtained it.

Step 3
Bitter Storm

Once Step 2 is complete, Step 3 immediatley begins and a storm will blow across the map, causing the freeze timer to rapidly increase in speed. The objective is to get halfway through the village before freezing. Once the step is complete, an actual survivor will open the door of a once unopenable building and tell them to get in. Once they get in, the step is complete.

Step 4
The Choice

The survivor reveals his name to be Harvey Yena, and he states that while he doesn't wish death on Richtofen, whatever he is planning is not good. A woman comes into the room, revealed to be Sophia. Harvey says that he knows a way to stop the Original Group from killing Richtofen, and to stop the Grand Scheme. The group will then choose to help Harvey and Sophia. Harvey will then say that they should find out what Richtofen is doing, and then they will sabotage it when the time is right. The group will then leave the house, Harvey closing the door. They must run to the Canteen before they freeze.

Step 5
The Dark

Richtofen will say that the Group should find a way to light the area. The goal is to press the use button on all of the lamps and lights in the village. The freeze effect returns to normal once the door is open. Richtofen reveals that the village is actually a Group 935 outpost, to keep prototypes from the Lighthouse Facility safe incase of an outbreak. Once the village is lit, the sky will gradually get darker over five rounds, the step ends when it is completely dark, bar the lights.

Step 6
Frozen

Richtofen states that the Generator, when hacked into, will reveal the information that Richtofen needs. The Generator is located at the top of hill leading down to the Submarine's lake. To 'hack' it, the use button must be used for thirty seconds straight, while other players cover the hacker. Once this is done, a hologram will burst out of it, showing a complicated map of an unspecified area. A rectangular object will then glow on the generator and make a loud beeping noise.

Step 7
The Icy Cartographer

Zombies will then charge the Generator from the village, whilst none will spawn near the water as they do in normal rounds. The goal is to protect the Generator for three minutes. Once this done, the object will pop out of the Generator and must be picked up with the use button.

Step 8
What Lies Ahead

When the use button is used on the object, Harvey Yena will appear, pushing the player aside and grabbing the item. He will then whisper that the group should lie to Richtofen and he quickly flees back into the village. Richtofen will then ask whether the group got the object, to which they reply yes. Richtofen will then giggle, and give his rewards.

If the players go to Harvey's building, Sophia will hand each of them an L-1 FE Binder, which is now has an icy theme to all of it's form as opposed to a forest one.

Harvey will then say that he'll decipher the object and find out why Richtofen would want it.

Rewards
Richtofen will give all the perks, including their normal versions which persist through death, as in the previous Major Easter Eggs from Call of the Dead, Shangri-La and Moon. The Cold Effect is also reduced greatly, aswell as the night sky remaining for the rest of the game.

Harvey's reward is the L-1 FE Binder, and is only obtainable by going to his building. The achievement is also only unlocked by someone getting the L-1 FE Binder.

Trivia

 * Harvey and Sophia were originally not going to appear.