Call of Duty: WWII

So this achievement requires you to build the Tesla Gun and its 4 different upgraded versions, Midnight, Reaper, Bloodthirst, and Hurricane, and all variants must be built in the same game. You do not need to build all of them yourself, as soon as they're all built everyone in the game at the time will get the achievement anywhere from a few seconds to minute after building the last one. But I can confirm if you join the game in progress you will not get the achievement. Even if you're there from the start and then lag out, then join back in, you need to be in the game from start to finish to unlock the achievement. This can all be done solo, but it is easier with more people (assuming everyone in the game knows what they're doing) but unless you really know how to build each variant by heart I highly recommend you do play solo so you can pause the game and refer to any guides for any step of the Easter egg or obtaining the Tesla Gun upgrades as you play. It may tempting to try and knock out the Dark Reunion Easter Egg as well, since you need to build all variants to complete this egg, but I found playing just for this achievement first and learning how each upgrade works by memory made it so much easier when I tried to get Dark Reunion later with friends, because I could kind of lead the way on building the variants without having to stop and look at a guide every few seconds. It's up to you, I found it easier to learn how to do all of the steps solo since I could pause the game and refer to a guide as I went but it's up to you.

The original Tesla Gun is built after several steps into the casual Easter egg for the Fireworks achievement. Two of the Tesla Gun upgrades you can't even start working on until you have the original Tesla Gun built. In addition, you won't be able to finish any Tesla Gun upgrade until you've completed the step in the Fireworks Easter egg that requires you to defend the three lightning rods at the Tower (Though you can get started on some of them early on). If you haven't already gotten as far in that Easter egg as to build the Tesla Gun and defend the lightning rods at the Tower, I would suggest you make sure you know how to do that first, Powerpyx has a good video guide on how to do the Fireworks Easter egg, though you don’t need to do any more past defending the rods at the Tower for this achievement.

Fireworks Easter Egg:
Now as for the upgraded Tesla guns you'll be building them right at the same round table that you built the original Tesla Gun, in the command room. Each upgrade requires a unique Tesla barrel, and these are obtained in different ways. Powerpyx also has great video guides on how to obtain each Tesla barrel, familiarize yourself with each guide so you're clear on what you'll need to accomplish over the course of the game.

Reaper:
Hurricane:
Bloodthirst:
Midnight:
Now if you know how to complete the Fireworks easter egg past the part where you defend three lightning rods at the tower, and you know how to obtain each Tesla barrel, then you are ready, so what I want to do now is explain how you should work towards these upgrades and getting enough progress of the Fireworks Easter egg over the course of the game. That is of course unless you want to attempt this your own way. Everything else in this guide is a walkthrough of either how I did it or how I recommend you do each step to get these upgrades. This is just my way of doing it, it's not necessarily the best way but it worked for me and I hope it helps you too. If anything is incorrect or messes you up I apologize if it doesn’t help you and I'd appreciate it if you leave a comment explaining something incorrect or a better method for something so other people can see. If you want to use my guide I recommend you skim over it first just so you can plan ahead and know what you'll be doing before you're already playing.

First of all, make sure you have camouflage in your loadout (if you don’t have custom loadouts then choose medic). I also recommend adding the ability that makes powerups drop more often in your loadout if you can use custom ones, because powerups that max out your special will also help greatly because you'll be able to camouflage for a long time. I also had the abilities that helps my special fill up faster and let's me carry three primary weapons but these are all optional, of course.

CO-OP

My co-op guide isn't as cohesive as my solo guide since you're not going to be able to just stop the game and read or watch a video mid-game with other people, so I just want to give some pointers.

First of all I'm not sure about with two players but definitely with three players you will start to see Wustling (big arm) zombies at about Round 8, making the strategy to leave the salt mine door closed until you can get a Wustling and have him charge into the panel in the sewer to get that battery ready much more viable. Leave the salt mine door closed until Round 8, kill every zombie but the Wustling AND one regular zombie, and get him to charge into the panel (see Reaper video for help) and then open the salt mine doors have one person go down inside while camoflauged and shoot the zombies' back heads to make them drop their bombs, then train them to the sewers and set the trap. You'll need to do this one more time at some point in the game without an easy out like that, but at least that battery will be half charged which is good because in co-op I feel like this was the hardest battery to charge. To get the second charge you'll need to tell your teammates to call out bombers and, if they're good enough, have them shoot the zombies' back heads to drop their bombs. If you can all get two bombers with no bombs at once and get them all in the same train, then you've got the hard part out of the way and all you have to do is lead that train to the sewers, set the trap and make sure both of the bombers die in the trap.

Make sure you also get a bomber at some point that you can lead all the way to the panel in the lab that way when you start getting two or more Wustling zombies per round you can start charging that. (See Hurricane for help)

As soon as you get the Tesla Gun, save a zombie at the end of the round and then shoot the lights to get that battery that way you can charge it sooner than later and you're not waiting for pest rounds in the late 20s/30s (see Bloodthirst for help).

Midnight is easy to get if you can just get a good train of regular zombies, which of course are abundant so I would save this for last or while you're waiting for more bombers for Reaper.

Once all Tesla Gun variants are built the achievement should pop after a bit. It doesn't matter who built what or if some people didn't build any, and no one even needs to pick any of them up if you don't want to. Everyone who was in the game from the start should get the achievement.

SOLO

When you start the game, try and shoot zombies two or three times and then melee them for the first two rounds to try and maximize points, the more doors you can open and perks you can acquire in the earlier rounds could make things easier later. Work through the first steps of the Easter egg until you reroute power to the Salt Mine doors. DO NOT open it yet. Once you open it, four bombers will come out and we can use these to help with the Tesla upgrades. Just keep killing zombies and buying perks like double damage, increased stamina, increased reload speed, and quick revive, but also try and work the mystery box not only to get good guns but you definitely are going to want to keep hitting the box until you get the jack in the box (monkey bombs) because these will help a lot with defending the lightning rods and defending the Tesla barrel upgrades.

So leave the Salt Mine doors closed for now, until you get your first Wustling zombie (the big zombie with the large sword arm). You should get him around rounds 7-8. If you don’t then I recommend you restart. I didn’t when I was going for this and I didn’t get the Wustling until round 11 and it made it harder to the Fireworks Easter egg when I was already in the teen rounds I've read that they start appearing at Round 7 but I cannot confirm this. I keep getting them only at Round 11. If that's the case then you'll have to decide whether it is worth it to hold off on the Salt Mine doors until Round 11 just for that easy bomber trap or if you should get started on Fireworks now and work on that later. Once you have a Wustling zombie, kill every other zombie but leave 2, and I say that because if you leave just 1 it will start running and it will make trying to get the Wustling to charge into the gray panel a pain in the ass. Also make sure by the end of this round you still have a fully charged Camouflage, even if it's just yellow. Bring the Wustling to the sewers and let him charge into the panel as shown in the video guide (Reaper). Make sure to place the battery in its holder when you get the chance. Now, leave those 2 zombies but kill the Wustling, then open the Salt Mine door. Use you camouflage immediately and run down to the bombers. You need to shoot, not their heads, but the little head above the bomb on their backs, so they drop their bombs. You should be able to do this before your camo runs out then you'll want to walk with them right behind you toward the sewers so you can charge the battery in there by setting the trap when they walk right by the battery. Just make sure to keep them close until them, so one of them doesn’t despawn and then spawn somewhere else, with a bomb. If you did this correctly, the battery should be half charged, you'll have to do this one more time at some point.

So now you're going to want to go down into the Salt Mines and keep working on the Fireworks Easter egg, building the Tesla gun and such. Meanwhile there are three things you need to work on at the same time:

- Leading one more group of at least 2 bombers to the sewers trap to finish charging the battery (Reaper)
- Leading 1 bomber to blow up the gray panel in the laboratory, see the video guide if you don’t know where it is (Hurricane)
- Leading a group of at least 2 Wustlings into the trap in the Laboratory, twice (again, see Hurricane) this can only be done AFTER you lead the bomber to the panel, because the Wustlings are needed to charge the battery.

So which of these should you do first? I recommend trying to get that one bomber to blow up the gray panel in the Laboratory for that battery (Hurricane), because the earlier rounds usually will only give you one bomber per round, as you get into the later rounds them you'll usually get two or more, which you'll need to finish charging the battery in the sewer (Reaper). Once you have blown up the panel in the Lab and place that battery, make sure you save any Wustlings you get during a round. If you only see one, just keep killing other zombies and another one will probably spawn later that round, depending on how many rounds in you are. Remember, you need to do this twice. You can either try and save two Wustlings or try and save two bombers to get that last charge in the sewers (Reaper). Whenever you see a bomber, aim for the back head to drop their bomb so that you don’t have to worry about them blowing up in your face. Don’t forget to use camouflage to make it easier to do this. Also, don’t try and save 2 Wustlings and 2 bombers in the same round, you'll probably end up killing them all in one trap anyways so there's no point. Just try and work on these both as the opportunity comes but one at a time, and if you've completed both of these or you're still waiting for bombers/Wustlings, keep working on the Easter egg, getting the Tesla gun built and getting to/past the part where you defend the lightning rods at the Tower.

Once you have the original Tesla Gun, you may or may not be done with charging the battery for Reaper/Hurricane. That's OK, but the very next thing you should do now, with the Tesla Gun built is kill all Wustlings, bombers, whatever and leave 1 or two zombies and then start shooting the lights to get that battery (Bloodthirst). You need pest rounds to charge this battery so you want to do this earlier than later. If you have the battery before round 15 you're doing great, before round 20 is still good. I didn’t actually get started on this until round 30 and it was hell, don’t wait too long. This is because each pest round is every 5 rounds, and you need two pest rounds to charge the battery, so make sure the first thing you do when you build the Tesla Gun is to obtain and place this battery so you're ready to charge it on the pest rounds. Refer to Bloodthirst for how to charge it, what I did is I trained all the posts, ran into the morgue, then threw a jack in the box into the middle, then set the trap, did it two different pest rounds and it worked.
I saved Midnight for last because its easiest. By now you should have already killed at least one Brenner zombie (The big zombie with the flamethrower) you just have to find where you killed him, pick up his head and then shine it at a statue in the courtyard. You need the Tesla gun to shoot it off the base then all you have to do is train regular zombies and then trap them at the courtyard, pretty easy, any confusion just refer to the Midnight video.

Now, you don't have to wait until you have every battery charged to start creating the Tesla barrel upgrades, but you do need to have finished the part of the Easter egg at the Tower where you defend the lightning rods before you can actually place your charged batteries into the Tesla part stations. If you’ve already done that part of the Easter egg, then refer to the videos to see which charged batteries go where, you'll bring them either to the Laboratory or the Morgue, and then you have to defend them. This can be difficult as now the rounds are getting much harder and you can easily get overwhelmed trying to survive in the Morgue or the Laboratory. This is why you should have Camouflage equipped and hopefully you got the jack in the box by now. Once you start the battery upgrade process, just wait and kill a few zombies until a lot of them start running in the room, and then activate camouflage. Even if it's only charged yellow, it should be enough. Just kill zombies all around the room, and any that attack the battery and as soon as the camouflage runs out throw a jack in the box out of the room, then right when its about to explode throw another, then repeat. Now you've got no camo and no jack in the box so just run away because by now the battery should be done in only maybe another 10 seconds, the zombies won't be able to damage it enough to actually stop the process, so just run away wait until there's a few zombies left and then come back and grab the Tesla barrel. Bring it to the same table you built the original Tesla gun at, one of the compartments should open up and let you upgrade it. Now just run away because it takes a second to upgrade and that is not a good spot to stand with zombies coming after you. A big notification should pop up saying the objective was completed. When you can just run back to the Command Room and grab the upgraded Tesla Gun. You need to upgrade all of them but I recommend upgrading the Hurricane Tesla Gun asap because its very good and when you're defending the batteries you can shoot an energy field onto the battery before you run away to give it some extra time. So once you’ve upgraded a Tesla gun you'll need to build your Camouflage back up and you'll need a pest round or a random max ammo to get your jack in the boxes back (this is why its good to bring the ability that increases power ups drop rate). While you wait for a max ammo you can keep working on charging any batteries you haven't finished yet, and lugging them over to the machine so when you're ready to defend them you can just hold x on them and start the process.

Once you upgrade the last Tesla Gun you don’t even have to pick it up, just wait for it to build and them once it says objective completed the achievement should pop in a bit.

So that’s basically how I did everything and it worked for me, I did everything as I explained in this solo guide here almost completely, then had an easy time redoing everything in co-op while going for Dark Reunion. Like I said, if anything in my guide is wrong or you have a better method please leave a comment, and make sure you check the comments anyways to see what other advice or corrections people have. Thanks for reading and good luck with getting this and maybe Dark Reunion.