In fanfic writing and science fiction fandom, a Round Robin is a story that is being written in turns by several authors, usually rather randomly - i.e., someone writes the first part, puts it somewhere where other writers can see it, and someone else decides to continue it, and then someone else continues after that, etc. Basically, whoever feels like it at a time can write a part.
Now, this technique probably wouldn't work so well for a challenge level, as those need to be somewhat more deliberately planned out. However, it could work just fine for an environmental, I think. And there is one tileset that IMO is just screaming to be turned into a proper environmental: Smashy's tundra tileset. Seriously, has anyone ever used that for anything but a very small area in a larger world? Yet it is - potentially - such a very versatile tileset, and a very beautiful one, too! The best use of it that I can remember having seen is in Shawnachu's environmental level Natural. Every time I walk through the tundra/snowy mountain area there I wish it were larger - much larger.
So, why not have an environmental Round Robin based on that tileset? Let's say everyone who participates builds about five screens, and they have to follow somewhat organically from the adjacent areas, and that's it, for rules. Well, and obviously we need to take turns rather than everyone starting at once, because otherwise the parts wouldn't integrate well...
Two more... rules, or suggestions: 1.) Other tilesets may be brought in, but use them very sparingly, and only if they fit in with the tundra tileset in terms of style etc., and 2.) try to push the tundra tileset - I'm pretty sure that's a tileset that will go a loooong way if you push it...
Y/N? Remarks, suggestions? Questions?
Edited to add a screenshot from Natural.
ETA2: see text in italics.