Since I'm just a silent reader, I'd also like to share an idea and ask what you think of it. Imagine there are areas where there is some kind of "gas" or "fog" where it is not possible to breathe. This requires a breathing mask with a tank on the back that has a certain capacity. For example, if a zombie hits the player, there is a 25% chance that the hose will be damaged and need replacing before the player dies within 30 seconds. The equipment cannot be crafted, only found. The zombies in the area do double the damage per hit. I'm not a programmer and I don't know how difficult it is, but my naive thinking says: define the area for the zone, let zombies do more damage in this area. The item with mask and oxygen tank or filter, whatever, is of course also needed. And that's all. Tadaaa