Basically, you're looking to add a mob of similar strength to B rank Hunts, with the primary difference being that it has a fixed spawn location, and it's reward is RNG dependent to encourage long term camping, right? That's something I'd be interested in, I'm quite fond of hunting down glamours and minions. I do feel, however, that it could be tough to implement alongside Hunts without it feeling somewhat recycled. We already have a system that involves scouring the map for rare monsters, the only difference here is it drops a chest and you stay for a while once you find it.