Call of Duty: WW2‘s take on the franchise’s popular Nazi Zombies mode may provide more in-game clues for players to find its secrets and powerful weapons, but the game is a lot deeper than it appears on the surface. Players that truly dedicate themselves to Nazi Zombies in Call of Duty: WW2 will discover that there is a way to upgrade the Tesla Gun weapon, and doing so is required for anyone that hopes to complete its “hardcore” Easter Egg.

Before players can worry about upgrading the Tesla Gun in Call of Duty: WW2, they need to build the base one. For more information on how to build the Tesla Gun, please refer to our Tesla Gun guide. After the Tesla Gun parts have been collected and the weapon properly assembled, players need to seek out the upgrades, though getting each one is easier said than done.

Obtaining all the Tesla Gun upgrades is part of Call of Duty: WW2‘s most convoluted Nazi Zombies Easter Eggs, and so players actually have to complete a few steps of the Easter Egg before they can get started. Please refer to our Nazi Zombies Easter Egg guide and play to the point just after the lightning rod is powered at the Tower before going after Tesla Gun upgrades.

With these prerequisite steps complete, players are ready to seek out all the Tesla Gun upgrades in Call of Duty: WW2‘s Nazi Zombies mode.

Bloodthirst Upgrade

To get the Bloodthirst upgrade, first head to Riverside. There’s a streetlamp here that flickers and spits out sparks, so shoot it with the Tesla Gun. This will start a sequence where players need to follow green lights all the way around the map and back to the Morgue. Shoot each light one at a time until reaching the Morgue, where the Bloodraven battery will be found lying on the ground.

Pick up the battery and place it in the device in the corner of this room. The next step is charging the battery, which is done by killing pest zombies using the spike trap in this area. After enough pest zombies have been killed, retrieve the device and take it to the upstairs section of the Morgue, where it can be placed in another slot. Defend the battery from the next wave of zombies, and if done successfully, the Bloodthirst Tesla Upgrade can be retrieved and taken to the Tesla Gun assembly station in the Command Room (which is the room where the mystery box first spawns, for the uninitiated).

Hurricane Upgrade

Obtaining the Hurricane upgrade is a little easier than getting the Bloodthirst one, but it’s still no walk in the park. The first step is getting access to the Stormhaven battery, which is hidden behind a locker in the laboratory. The locker itself is against a wall at the bottom of the stairs, and the only way to open it is to bait an exploding zombie into blowing up near it. Lead an exploding zombie to the locker, blow it up, and then pick up the battery.

Place the battery in the designated area in the lab’s long tunnel with the metal flooring. For anyone having trouble finding it, this is the place where the electric trap is activated. Once the battery is in place, players need to simultaneously kill two of the larger, more powerful zombies using the electric trap. To do this, wait for a couple to spawn and kill all the other zombies around them to make it easier to bait them into the trap without accidentally missing one.

Once this has been done twice, retrieve the battery and take it to the machine in the lab. Just like before, defend it from the onslaught of zombies, and then collect the Tesla Gun part that the machine produces. Return the part to the assembly station in the Command Room to unlock another Tesla Gun upgrade.

Midnight Upgrade

Before starting this upgrade, players need to acquire a Brenner head, which falls off the flamethrower-equipped zombies. With a Brenner head in tow, head to the courtyard and aim it at the statue nearest the gate. The statue will crumble, revealing the Moonraven-Attuned battery. Shoot it with the Tesla Gun to knock it to the ground, then pick it up and place it in the nearby generator.

As one might expect, powering this battery is done by killing zombies near it with a trap. Use the mine trap in the courtyard to kill regular zombies to power the battery, and then take it to the machine in the Laboratory. Defend it from the new zombies that spawn, retrieve the upgrade part, and then take it to the Tesla Gun assembly station.

Reaper Upgrade

Check the sewers for a locker that looks exactly like the one players had to blow up to get the Hurricane upgrade. Blow it up by leading an exploding zombie to it and then go pick up the Deathraven battery. Place the battery in the generator, itself located near the Pack-A-Punch/Weapon Upgrade station.

The next step is tricky, as powering the battery requires players kill two exploding zombies simultaneously with the sewer’s saw traps two times, for a total of four dead zombies. The problem is exploding zombies like to…well, explode, but there is a way to prevent this. Shoot the smaller zombie strapped to their backs to make them lose their bomb, which in turn will allow them to be killed by the saw traps without the threat of them exploding before the trap can kill them.

When that’s done, collect the battery and take it to the machine in the Morgue. Defend it from zombies, collect the weapon part, and take it to the Tesla Gun assembly station in the Command Room to get the Reaper upgrade for the Tesla Gun.

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While obtaining all the Tesla Gun upgrades in Call of Duty: WW2 is quite the challenge, taking the effort to upgrade the weapon is well worth it for hardcore players. Upgrading the Tesla Gun will not only leave players with a superior weapon, but doing so is required to complete the hardcore Easter Egg. Furthermore, obtaining all the Tesla Gun upgrades will earn players the Dark Arts achievement/trophy as well.

It may take players a few times through The Final Reich map to properly learn its layout before they are skilled enough to get all the upgrades, but they should succeed with enough practice and perseverance. And once they manage to collect the Tesla Gun upgrades, they should have an easier time killing zombies, reaching higher rounds, and completing the complicated “hardcore” Easter Egg.

Call of Duty: WW2 is available now for PC, PS4, and Xbox One.