Honesty, I wouldn't add a gun but instead focus on increasing the threats the monsters hold. I reference them as redeads from LoZ wind waker and maybe you could use those enemies as a sort of template for mechanics moving froward. I think it's be very interesting if the enemy reacted to sound in way that made them question about what's around them, like having them stop when you create a little too much noise and look around a bit before resuming their path. I think I'd also be a cool detail if they made subtle cries or sounds when the player were near them. Other than that the game is really good.