Upgrading Klaus & The Train Step
At this point, we need to upgrade Klaus. You need to call in Klaus once again and get him to kill as many zombies as possible. Since the upgrade is done in the Garment Factory, the best approach is to train a horde of zombies on Korber Rooftop and then use the yellow radio to call Klaus.
These yellow radios are scattered all around the map and can be used to call Klaus without having to go all the way back to the safe house.
Let Klaus kill all the zombies, and once he is ready to be upgraded, you will hear a distinct sound.
When you hear the above sound, that is your cue to command Klaus to the Upgrade Station in the Garment Factory.
You will also notice that the screen on the upgrade station has now turned green. It was red before the sound.
Klaus will go into the station, and you will need to defend him for one minute as he gets upgraded.
Once Klaus upgrades, he will come out of the upgrade station with a pack-a-punched weapon. The pack-a-punched weapon indicates that he is now upgraded to tier I. You only need a tier I upgrade for this easter egg. If you're looking to upgrade Klaus further, feel free to check out our dedicated guide on how to fully upgrade Klaus here.
After upgrading Klaus, go to the Ghost Station and command Klaus to stand on the train track furthest away from the Mule Kick perk machine.
As Klaus gets there, go to the Switch Control Room and use the Railway Switch to switch tracks.
Klaus will come to the train track and stop an incoming train.
You need to quickly get on the train and collect the bomb and Rico's keycard.
You can use the Aether Shroud ability to get these items from the train safely, and you might get overrun by the zombies.
The Uranium Step
Go to the safe house and use Rico's keycard to access the computer on the table in the middle of the room.
Interact with the computer three times to browse through the files, and you will eventually see a red screen.
Go back up to East Berlin Street and interact with the computer in the military tent in front of the electronics store to activate the disruptor satellite.
This will spawn some high-value targets (HVTs) similar to the ones seen in the Outbreak mode. The first group of HVTs spawns next to the pack-a-punch machine in the middle of East and West Berlin Street.
While avoiding the majority of the regular zombies, kill the spawned HVTs, including the regular zombies from it and the Mimics (really strong Mimics).
The most important zombie here is the Megaton. It is recommended that you lure the Megaton next to the military tent on East Berlin Street first and then kill it. When you kill the Megaton and the split bombers, each bomber will drop a Uranium Rock.
As soon as you kill one of the split zombies, a five-minute timer will start and the split zombies will drop the Uranium Rock. You need to complete the following step within five minutes, or else the game will end.
Pick up the Uranium and take it to the East Berlin Street military tent. Note that your health will slowly deplete carrying the Uranium Rock.
When at the military tent, use the Uranium Rock to craft a Uranium Device at the crafting bench.
Pick up the Uranium Device and take it up to the Destroyed Penthouse.
The best route to take from here is by using the rope directly in front of the military tent, which takes you back to 5th Floor Apartments, the spawn location. The rope is in between the entrance to the bar and the electronics store.
Go up to the Apartment Rooftop and use the zipline to reach the Destroyed Penthouse.
Place the Uranium Device on the zip line leading to the Korber building and then make your way back to the second Uranium Rock.
Pick up the second Uranium Rock, craft the Uranium Device at the tent, and take it up to the Korber Rooftop.
The best way to reach Korber Rooftop is through the rope in the Alley directly South of the military tent.
When you reach the Korber Rooftop, place the Uranium Device on the zip line leading to the Destroyed Penthouse.
Now, both the Uranium Devices will slide towards each other and collide.
Go down to the middle of East Berlin Street, and you will find Cleansed Uranium.
Pick it up and bring it back to the secret lab. You already have the bomb from the train. Interact with the conversion unit to first place the warhead inside.
Then insert the Cleansed Uranium into the conversion unit.
Now, you need to repeat the same step once more, but to be able to do it again, you need first to end the round.
End the round and then on the next round go to the military tent on West Berlin Street.
Use the computer to activate the disruptor satellite for another batch of HVT.
This they will spawn on top of Apartment Rooftops (the spawn point).
Go to the spawn point and eliminate all the zombies except regular and Megaton. Do not even split the Megaton. Leave the Megaton and go back down to the military tent on East Berlin Street.
When you are far away from the Megaton, he will teleport to you. Since you are near the military tent on the east side, the crafting process will be easier and faster since the Uranium Rocks will be near the crafting bench.
You can still craft at either one of the military tents. But the one on East Berlin Street is preferred as both the buildings are close to this tent.
Repeat the same and collide both the Uranium Devices to get Cleansed Uranium.
Pick up the Cleansed Uranium and bring it to the secret lab. Now, if you're already prepared with all the perks and necessary preparations, such as the tier III armor and a pack-a-punched weapon for the boss fight, you may insert the Cleansed Uranium into the conversion unit.
As soon as you insert the Uranium, there's no going back, and the boss fight will begin. This is a point of no return.
If you're not prepared, it would be best to drop the Uranium in the lab and do your necessary preparations before you enter the boss fight.
Read on to see the preparations you need to make for this boss fight.
Before you get into the boss fight it is highly recommended that you have the following perks:
- Mule Kick
- Speed Cola
You can also get Quick Revive if you have the points. As mentioned before, you can also get the Quick Revive perk in the middle of the boss fight. Ammo is one of the biggest issues during the boss fight. Mule Kick (tier II) helps with ammo by giving us a small chance of ammo drop when eliminating zombies.
You must keep Aether Shroud for the field upgrade and not change to Ring of Fire as most people do. Aether Shroud makes this boss fight a lot easier.
For the armor, you should have tier 3 armor by now either way. But, just in case you haven't, go to one of the arsenals and upgrade your armor to tier 3.
You will be using the base variant of the wonder weapon to take on the boss on this map. Make sure you have pack-a-punched your wonder weapon at least twice.
Also, before beginning the boss fight, grab another endstation lure as it can help you with ammo in case you run out. If you ever run out of ammo during the boss fight, throw the endstation lure to spawn three Tempests and kill them get ammo.
When ready, go ahead and insert the Cleansed Uranium into the conversion unit and be ready for the fight.
Valentina will come out of the huge portal in the middle of the secret lab.
When you see her health bar show up, start shooting at her shield bubble with your wonder weapon until it breaks, and continue firing shots at her to deplete her health.
As with any boss fight, the regular zombies will continue to spawn. Keep taking them out as you shoot at Valentina to fill your Aether Shroud field upgrade. The regular zombies will be dead in a single shot with your wonder weapon.
Keep shooting at her, and as soon as Valentina goes for her ranged attack, activate your Aether Shroud and continue shooting at her.
If your Aether Shroud ability isn't recharged fully before her next ranged attack, run away from her until she finishes her attack. Her ranged attack does serious damage to your armor and reduces it by a lot.
Valentina will also spawn some floating zombies around her that she uses to heal herself. As soon as she does, quickly take them out and do not give her a chance to heal.
She also spawns in Tormentors. If your surrounding environment gets all "reddish," it's a sign that she is spawning the Tormentors. Continue shooting at her even during this stage. You can shoot the Tormentors when they get a bit close to you.
Continue the same shooting strategy and shrouding during ranged attack until she becomes immune and teleports to the next location.
Another critical point to take note of is Valentina's wipe attack. This is an attack she does when your whole screen gets hazy with electricity showing all over your screen. This is an indication of her wipe attack.
As soon as you see it on your screen, quickly hide somewhere out of her sight, or else you will instantly drop down to 1 health.
In this complete boss fight, as her health depletes, she will teleport to four different locations before finally returning to the secret lab.
You can also go ahead and repair your armor in between the fight when she teleports. If there is an arsenal on the way to her next teleported location, you can repair your armor or even buy perks.
If you do not get to Valentina after a minute or so, she will teleport you to her.
You can also teleport to her by firing at her orange aura/bubble from afar.
One of the locations she teleports to is the destroyed penthouse. There is a Quick Revive perk machine. If you have enough points, do buy it. It will help you regenerate your health faster. If you already have the previously mentioned four perks, then Quick Revive will cost you 4,500 points.
Valentina will teleport to three different locations before finally returning to the secret lab, where you will deplete her health for good. The four locations she teleports to are:
- West Berlin Street
- East Berlin Street
- Destroyed Penthouse
Once her health is zero, she will fall to the ground, and you will get a prompt to 'capture' her when you stand near her.
Interact with her, and a mini cutscene will play.
Outro & Outro Cutscene
In the mini cutscene, you will see Klaus approach the bomb, pick it off the conversion unit, and start walking towards the portal.
You will again get control of your character. Now, you need to defend Klaus from a wave of incoming zombies until he reaches the inside of the portal.
When Klaus reaches the portal, zombies will stop spawning, and the bomb will explode, closing the portal. This concludes the easter egg followed by an outro cutscene.