Seal the Deal is the easter egg achievement for the map Die Maschine in Call of Duty: Black Ops Cold War. It requires players to close the rift that has been opened at the Projekt Endstation facility by the Omega Group. The Aetherscope and all of the upgrades for the Decompressive Isotopic Estrangement Machine must be completed beforehand. Note that while the Cryo-Emitter and NOVA-5 upgrades can be completed before the Aetherscope is built, the Electrobolt and Thermoplasmic upgrades cannot.
Once the Aetherscope is crafted, the player must enter the Dark Aether through the anomaly that spawns at the Medical Bay. Once in the Dark Aether, there will be a diary written by Doctor Vogel. When picked up, a "spectral reflection" anomaly will appear near the sink. Once the player interacts with the anomaly twice, a stronger version of the Megaton known as the Mayak will spawn. While the Mayak spawns, a sequence will play featuring a flashback to Doctor Vogel discussing his study of the various reanimated men that have been transformed by the Dark Aether. After the sequence is completed, another spectral reflection will spawn at the Control Room. Once the second spectral reflection is completed, a third and final reflection will spawn at the Particle Accelerator at the crafting table where the Aetherscope is built. Once the final sequence is finished, the player must wait until they exit the Dark Aether and return to the Medical Bay to interact with the computer where the diary was first collected.
Ensuring that all D.I.E Machine upgrades are completed, there will be a container within the medical bay. If the player is facing Speed Cola, the right leg of the container must be shot with the Electrobolt, and the left must be shot with the Cryo-Emitter. On the other side, the right leg must be shot with the NOVA-5, and the left shot with the Thermoplasmic. Once this is completed, the player must enter the Dark Aether through the anomaly that spawns at the exit of the Medical Bay, and must interact with yet another spectral reflection that spawns on the catwalk of the medical bay. Once the spectral reflection completes, the players will be returned to the Dark Aether where a Dark Aether Wrench will spawn which must be collected.
Once the wrench is collected, the player must head to the Yard where they will be able to interact with a tank with the wrench three times. A zombie will pop out of the exit hatch of the tank. This zombie must be killed to continue the quest. After the zombie is dispatched, an explosive must be thrown at the hatch, causing the tank to fire a shot. There will then be a Decontamination Agent at the Crash Site which must be brought to the Containment Unit in the Medical Bay. Note that the player will be unable to run or defend themselves while holding the Decontamination Agent. The player must then wait for a Megaton to spawn so that they can defeat it to get the Megaton Bomber and Blaster. The two Megaton halves must then be led one by one to the container so that they can be sucked into it. Once they are both in the container, the player must then interact with the computer in Medical Bay to begin the decontamination process. The player must then head to the "Living Room" inside of the Nacht area and interact with the Dark Aether anomaly that spawns there. Another spectral reflection will then appear in the corner of the Omega Outpost room that must be interacted with. After the sequence is complete and the player is sent back from the Dark Aether, an "Orlov Family Photo" will spawn that must be collected.
Once the photo is collected, the player will be teleported back to the Particle Accelerator where they will meet with a noncontaminated Megaton named Orlov, who once worked for the Omega Group. He will agree to help the player in closing the rift that was opened at the facility. He will then begin a sequence where he begins to deactivate the particle accelerator. Orlov must be protected from the various zombies, Plaguehounds, Megatons, and Mayaks that will spawn in the area. This will repeat a total of 2 times until the accelerator is deactivated. This will begin an exfil as energy bursts spawn across the map. The player must then make their way to the exfil area without hitting any of the bursts (which will cause them to instantly go down). The player has a minute and a half to do this. Once the player makes it to the Pond, they must interact with the helicopter and a short cutscene will play of the player leaving the facility as it explodes. The player will then get 5000 XP and a notification for completing the challenge "Evil Unleashed" for completing the main quest on Die Maschine, as well as the achievement.