For real world locations, they would fall under
MarioWiki:Generic subjects. And, as such, would need to meet any of 1, 3, or 5 to qualify for an article. 2 and 4 can't be used because these games fall under the sport category, with 4 being more likely of the two to be used with these locations, as 2 refers to collecting and consuming. For reference, the three we can use are:
1. The subject must have a function which is different from the real world counterpart. If the differences are extremely minor, the subject may not meet this requirement.
3. The subject is significant to the media's storyline.
5. The subject is determined by the users to be notable.
And these can be created or deleted without a proposal except for those which are deemed to be 5, where a proposal would only be needed to determine, especially if users can't agree on it.
As for the other locations, they fall under
MarioWiki:Coverage. Which state that everything should be covered. And I would agree on everything except for maybe the Sonic locations. Mario & Sonic locations are good because they have Mario aspects, but Sonic locations are purely Sonic. We should determine whether or not we really want to cover them. If not, then we will need to change MarioWiki:Coverage with a proposal. If so, we could just create them unless there are those who think that we don't create them. In which case, a proposal would need to be created.
And now the interesting part: Mario locations. Locations that are exclusively Mario. How do they fit? Well, if it is clear that they are existing, they should appear on that existing article in some way or another. If it is similar to the article, then it mentions a brief section with a link to the event. If it is not similar, either two things can happen. Either they can be an entirely new section covering every difference on the location article, or they can be covered on the event page and a small section about it appearing in the event on the location page (like Moo Moo Meadows is briefly covered on Moo Moo Meadows and the full layout is on the Dream Equestrian page). I am fine with either case. As for Mario Circuit, I am not entirely sure what to do either. It seems like if we want to do something, it could: be a new article, go on Mario Kart (Wii) article, stay on Mario Circuit with it expanded, or have the information on the events. The order they appear in are from me liking the idea the most to me liking the idea the least. As for the new locations, I go over the ones I know. Cheep Cheep River and Synchro Battle Galaxy should be given a full article, as they are unique. They are only covered in their articles because Dream Rafting has World 4-1 (New Super Mario Bros. Wii) music, and Dream Spacewalk has Sky Station Galaxy 1 (Super Mario Galaxy 2) music. Thus it makes them seem like they are from those games. But they aren't. They are just the music used. Yoshi's Picture Book is different then any of them. Yoshi's Picture Book is based on Rail Lift. But the Dream Long Jump article links to the entire book. And no matter what, what is on Dream Long Jump has the location description currently. As for Snow Colosseum, it sounds like it should be created, but I have no idea because I haven't played that game. Same for the first two on that list.