Call of Duty WW2 Zombies: How to Get Reaper Tesla Upgrade Variation - needed for "Dark Arts" trophy & achievement.

PREPARATION STEP (BUILD NORMAL TESLA + LIGHTNING ROD DEFENSE)

Before you attempt this, do the normal main easter egg . You must complete the main easter egg up until the Lightning Rod Defense.

Step 1 (Let Wstling Charge at the Locker in Sewers):
Go to the sewers, the underground area with the bloody water, where you also find the Pack-a-Punch Machine. There is a locker on the wall on the opposite side of the MP-40 wall-buy. It looks like a small metal door. Now you need a Wstling (big slow brute) to charge into the locker. This is best accomplished by standing in front of the locker, shoot the Wstling so it charges at you, and just "take the damage". It won't kill you if you have a full health bar. This is the only way to ensure the Wstling will hit the locker properly. When he hits it properly the locker will open up and reveal a battery that you can pick up.

Step 2 (Get Battery):
Plant the battery in the contraption just in front of the locker (2 meters away).

Optional Step 3 (Make Bombers non-explosive):
For the next step you will need 2 bombers alive. The problem is that they blow up when you get too close to them. One way to prevent this is to shoot the small head on the back of the bombers, the small guy holding the bomb. When you do this the bomber drops the explosive canister and can no longer explode, but he's still alive running around the map. It is highly recommended that you do this. It's easy to do when using the Camouflage ability. Tell all players (if you're playing co-op) to leave the bombers alive, use camouflage and shoot the small heads on the back of the bombers.

Step 4 (Simultaneously kill 2 x 2 Bombers using Saw Trap in Sewers):
You must kill 2 bombers simultaneously using the Saw Trap in the Sewers, when the bombers are standing really close to the battery. The battery must light up green for it to count the kills. This is the trickiest step of all the tesla upgrade variants. As mentioned in the previous step, it's highly recommended that you shoot the small faces on the back of the bombers so they drop their explosives and can no longer blow up. The problem here is, that there's a relatively big distance between the battery and the trap activation. There are actually two trap activation points. You'll want to use the one closest to the battery, near the locker (not the one by the MP-40 wallbuy). With 2 players you can have one person train the bombers and another activating the trap when the battery lights up green. This step needs to be done twice. So that's 2 x 2 bombers = 4 total. If the bombers don't die close enough to the battery you'll have to repeat it. It only counts when you kill 2 at the same time. Killing only one bomber does nothing.

Step 5 (Lightning Rod Easter Egg Step):
If you haven't already, complete the main easter egg up until the Lightning Rod Defense. Only after defending the Lightning Rods you can continue with the Tesla Upgrade.

Step 6 (Defend Battery):
Once the battery is powered up, pick it up (you'll know it's powered up because you can interact with it and pick it up). Insert it in the machine in the morgue that previously gave you a part for the normal tesla gun. Hold the interact-button to close the hatch. Now you must defend the battery for about a minute or so. Zombies will attack you and also attack the battery itself. There's a health-bar on the battery, the zombies aren't allowed to destroy it.

Reaper Upgrade Complete: After successfully defending the battery, pick up the part from the machine. Now you can return to the Tesla Upgrade Station in the Command Center (Bunker) to build the upgraded Reaper Tesla Gun.