Here's a wild guess. When I first looked at this helmet, I immediately thought of a persona known as Chernobog, from the Persona series. Chernobog is known for his fungal-like appearance in Persona, and he is known in Slavic culture as the god of death. The design of this helmet reminds me of some sort of fungus, which is what led me to this. Fungi are also known as decomposers as well, obviously, so it kinda loops back.