On this page of the Resident Evil Village game guide, you will find a walkthrough of the puzzle that involves creating the Heisenberg's Key necessary to explore further rooms of the Heisenberg 's Factory. You will learn where to get the mold needed to create the key, where Heisenberg's Key can be created, and what it is used for.
Acquiring the Key Mold
You will have to find out how to acquire Heisenberg's Key once you begin exploring the Heisenberg's Factory, a location visited in the final stage of the campaign.
Ethan must go through a very large part of the factory and ultimately reach the level B1 room pictured in the images above. You will find the Key Mold within.
Creating Heisenberg's Key
Bring the mold you just found to the Casting Machine located in the Foundry room on level MB4. Ethan visited this place earlier in the game, but he didn't have the necessary quest item with him back then.
Use the Key Mold and wait a while for Heisenberg's Key to be created .
Purpose of Heisenberg's Key
The key has two main uses. You can use it to unlock the optional Heisenberg's Quarters room on level MB4. There are some regular monsters inside and once you dispose of them, you will find lots of small loot and a Mechanical Part (Shaft) treasure that can be combined with the Mechanical Part (Cylinder) treasure that can be found in a different part of the factory.
The most important use of Heisenberg's Key is to open the door on level B1, near the elevator. This will allow you to continue the game and reach the Prototype Sturm boss fight.