The Outbreak zombies mode is not short of easter eggs and objectives. While the main and side objectives are clearly indicated on the map, some "secret" side easter eggs require equal amounts of work and luck to complete, thanks to the RNG (random number generation) involved.
One such side easter egg is the Demented Echos zombies easter egg specific to the Outbreak mode in Black Ops Cold War zombies. This easter egg also has a unique calling card associated with it, for bragging rights, as completing this side easter egg is no easy feat.
To complete this easter egg, you must find a total of ten demented echo zombies while playing the Outbreak game mode. These fiery hot (literally) zombies spawn randomly in each region in a set number of locations. But, only one spawns at each difficulty level. This means if you find one during difficulty level 1, you can only find the next one on difficulty level 2 in whatever your next region is.
When you find these zombies, you must keep your distance and approach them slowly, as they will suddenly lunge towards you. If they manage to reach you, they explode, setting you on fire and spawning many regular and elite zombies. You must kill them before they reach you.
Upon successfully killing the demented echo zombie, you will get a "hush" medal. You must get ten "hush" medals to get the "Restful Spirit" calling card as a reward.
This guide shows you all the demented echo zombie locations that we've managed to find so far in each region. There could very well be more than what we've stated below. Feel free to comment below if you find new locations!
The first demented echo zombie can be found in a cabin located at the Old Farm.
The second demented echo zombie can be found in an elevated shack located in the middle of the woods. The specific name of the location is Backwoods.
The third demented echo zombie is found in the office cabin located at the Cargo Platform area.
The fourth demented echo zombie is found inside the Base Headquarters' main building by the Rocky Hillside.
The fifth zombie is found inside one of the tents at the Mobile ICBM Site.
The first demented echo is found inside one of the garages located at the First Aid Station.
The second zombie is found under the Chalet platform.
The third zombie is found inside one of the Base Cabins. It is the far-right cabin, to be specific.
The fourth demented echo zombie location is inside the orange cabin you come across at the Ski Patrol. The zombie will be on the second floor.
The final location is the top-most floor of the main lodge. We couldn't get the zombie to spawn due to the spawns' extreme RNG nature, but the marked location is 100% correct.