Desert regions
After reading that, the zombie event in iria desert immediately came to mind for a location. Assuming this were done i think that'd be an excellent start point. Just scatter camps throughout the desert, players can join and spawn in camps.
As for the honest method of control and flow of combat, i'd be interested in hearing more on that. Example, ignoring the difficulty to implement this and just throwing it out, players home base being the side of desert closest to rano. Progress away, to the north side of desert. Players don't just make an instance, but rather it's an ongoing fight, as long as there's a player in the area, maybe with a time limit to reset the area.
As you progress density of mobs increases, strength increases, rewards increase. And
intentionally put groups of mobs together that are meant to be mean and multi. Shadow wiz is a good example of a mix, with varying types of mobs. That's just an example though, expanding it further would be interesting.
I'll stop there though, i could ramble on about what i'd like to see, but that's plenty for getting a general grasp of my train of thought i think.
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