The End? is an achievement featured in Call of Duty: Infinite Warfare on the zombies map The Beast From Beyond. It requires the player to collect the fifth and final piece of the Soul Key. If you do this while Director's Cut is active and after completing the Talisman Mask quest, you will be fighting Mephistopheles instead.
Step 1: Powering the Station
The first step is to acquire N31L's head. You need to reach the Ops Center, where you can find a hole. Jump down the hole to a ledge where you will find the Tuff Nuff machine. Proceed through the path until you see N31L's head on the ground. Get it and go to the spawn room, putting his head into a terminal.
Step 2: Obtain the Disks
Now you need to obtain four Disks that are scattered around the map and put it on the terminal following a specific order. The first Disk is dropped by the first Phantom killed on this match (either the one that spawns when you enter the Projector Room for the first time or the first one that spawns on Round 10), so watch when he is near. The second Disk is found by the left side of the Projector Room's portal. For the third and fourth Disk, you need to get the Entangler. After that, for the third one, go to the room where you can find the Proteus and the fuse box. You will see a red corridor with some smoke. Use the Entangler on the ground when you see the Disk. Now throw it on the smoke. This will make the Disk appear on any vent around the base. Now for the last Disk, go to the Spawn Room and use the Entangler to pick a Astronaut Helmet. Keep holding it until you reach the room where the dead Cryptid is on the table. Throw the helmet at the green monitor to shut the wall down. After that, you can find the Disk by a table.
Step 3: Enter the Disks
Now, you need to enter the four Disks on N31L's terminal. By the Spawn Room climbing a ladder, you will find a paper on the ground with some Symbols, read it from left to right. Near the UP 'N Atoms will be another reference, reading from top to bottom. Now go to the Cafe area and you should find some papers by a table, read it from left to right (or from up to bottom). Now go to the Computer Room leading to outside of the base and near the red buttons used to get the Venom X Upgrade will be some papers with symbols too, read it from up to bottom. Now, after you've seen all the papers, match the order with the Disks at N31L's terminal. The order of the Disks should be from left to right, following one of the references. Check the first symbol, if its not one that is in the game, move to the second one. The order will always be the one that comes first (EXAMPLE: If the first symbol on the paper is a triangle but the second one is a diamond-like and one of the four Disks is the diamond shaped, you should put it on the first slot). If you insert the wrong combination, some Cryptids will spawn and the Disks will return to their spots. If you make the right combination, he will freak out, opening and closing doors while activating traps.
Step 4: Hacking N31L
When N31L starts to go crazy, go to the real life Theater and find the Brute. Looking out of the border of the map, you will see a lampshade. At the right side of this lampshade, you will see a button on the wall. Pick this button with the Entangler and carry it to the Afterlife Arcade until you see a "The Beast From Beyond" poster. Get closer to it and throw the button inside the poster. If you do it right, the button will be dragged inside the poster and you will find it beneath a table at the same room where you got the last Disk. Pushing this button will enable you to move some dials near the dead Cryptid on the table. You should move the vertical dials to horizontal or all the horizontal to vertical.
Step 5: Moving N31L's Head
After you finish with the dials, N31L will now be hacked. Go to his terminal and when he shows the happy face, grab him with the Entangler and move him up until you reach the portal to the Projector Room. He is still rogue, so the doors are opening and closing frequently and zombies will keep chasing you. Doing it wrong will Nuke the zombies and possible ending the round. Carry his head to the Projector Room and carefully put his head inside the monitor. After his head is inside the computer, the process is complete and interacting with him will teleport you to the boss room.
Step 6: The Cryptid Swarm
As said before, interacting with N31L inside the Pack a Punch room will teleport you to the boss area. Initially, you will be in a closed space with some containers. Now, N31L will start shooting some of them. The first four shots will open one container each time, launching a Cryptid Rhino. They have huge HP and very high damage, specially the charge attack. When the third Rhino is freed, his container will leave an opening to the back area. After the fourth Rhino is killed, there will be some seconds to rest up. Now all the portals will turn on and some Cryptid Scouts will start to come out. Dealing with the first swarm will open another area. There will be more portals and now the Cryptid Phantom will start to spawn, as a reminder, they can kill you with 3 hits, can teleport but don't have too much HP. The area will be almost open when they start to appear and you will need to survive the second swarm. When the second portal section is open, you can find some Sentry Guns scattered around, this will help you finish the swarm as well as an ammo box at the initial section of the Rhinos and some Candy Perks near the up area (the perk area will be the last section to be accessible). Now finishing the second swarm, Rhinos will start to pop out of the portals and N31L will start shooting at you as well. When the first Rhino spawn, after some seconds there will be three terminals turning on near the portals section. You now need to turn them off in a quick time frame. When it's done, finish the remaining Cryptids and run to the ammo box and rest a bit. N31L will keep shooting and eventually he will open a container with another terminal. Stand still and wait for the terminal to turn on. It will show a Countdown from 99 to 0. You will need to survive a third swarm, bigger than before with several Phantoms, Scouts and some Rhinos. When the countdown is over, interact with the central terminal again. The room will get darker and after some seconds to breathe, two Cryptid Mammoths will finish the fight. They have an insane amount of HP, dealing the same damage as the Rhinos but they can set the ground on fire. The blue fire they can spill deals very high damage per second and stays way too long of the ground. Some Cryptids can spawn too along the fight. You need to control the fight to avoid the flames and their charge attacks. After you've deal with the two Rhinos, the ending cutscene will play.