Alternate World.

[StandbyForBattle]

In Sun/Moon, You can enter an alternate world, where you can catch the pokemon depending on what version you have. For example, If you bought Sun, you have to catch Solgaleo in the Main Story and Lunaala after you defeat Lusamine, and have Solgaleo in your party, then a wormhole would open, then you'll be able to catch Lunaala. In UltraSun and UltraMoon, I wonder if you can enter the Alternate World in SM or you'll enter in a Alternate World depending on what version you'll get again. If so I wonder what we'll change in US/UM from the event of Sun/Moon?

 

[Silktree]

Chances are that SM's alternate worlds are just the USUM worlds (Moon goes to Ultra Sun; Sun goes to Ultra Moon). So in USUM it should work the other way around.

What that entails for the content... who knows.

 

[StandbyForBattle]

Maybe US/UM will have a Alternate World from the events of SM.

 

[Cookies and Creme]

You can't catch Lunala in Sun as far as I know. I played Moon, and my Cosmog just evolved into another Lunala. I tried it both in the alternate world and in my own world.

 

[GiraFragMich]

Currently about half of the national dex is native to Alola/can be caught. With GF being known as making the majority of the national dex available within a generation I can see them trading out most of the Alola dex (bar Gen7 Pokemon and regional variants) for substitutes. Species not yet available in Alola but only through transfer. This would make sense as several made-for-Alola Pokemon were not in Su/Mo as Solrock/Lunatone, Mantine, Bellosom etc.

I also think that several Pokemon being in the Alola dex now will have regional variants in the alternate world, like Drowzee and Machop line.

This would make for a new experience while exploring the islands.

 

[Morningstar]

Currently about half of the national dex is native to Alola/can be caught. With GF being known as making the majority of the national dex available within a generation I can see them trading out most of the Alola dex (bar Gen7 Pokemon and regional variants) for substitutes. Species not yet available in Alola but only through transfer. This would make sense as several made-for-Alola Pokemon were not in Su/Mo as Solrock/Lunatone, Mantine, Bellosom etc.

I do think this will likely be the case, but the thing is that they still would have to find a way to make at least 100 mons catchable even if they decided to replace everything int he pokedex but the Gen 7 pokemon (itself unlikely due to various factors), as well as the Island Scan pokemon. There isn;t much room to replace pokemon partly because only half of the national dex (and partly because USUM is not a remake of a past game, would would free up more slots since they no longer have to use Alola-native pokemon)

BW2 did manage mostly without the Pikachu line, the Gen 3 Mascots, Mewtwo (the Legendaries at least had events) and Unown, but they had less pokemon to work with and the benefit of having 2 spinoffs to catch the rest (Dream World and Radar). For Sun and Moon to be able to fit the other 400 pokmeon, I feel an updated version of the Friend Safari, the Island Scan and a certain ORAS plot device might be nessisary, but I made a whole post on that in another thread.

 

[IncineROAR]

I think the "alternate worlds" are much like the different Unova's between Black and White (the same but different), RSE/ORAS, and SM (Sun versus Moon, 12 hr difference). The whole multiverse argument - I think that is what USUM will be to SM. Similar but different worlds.

 

[Mitchman]

Chances are that SM's alternate worlds are just the USUM worlds (Moon goes to Ultra Sun; Sun goes to Ultra Moon). So in USUM it should work the other way around.

What that entails for the content... who knows.

Which is why I think it can work as a sequel/3rd version deal. To save space and not give things away it seems like the events of SM also happened, but in reality the second cosmog you gain in game is why Necrozma is now plot relevant, as the SM protag popped up and creates the disappearance of the regions protector. USUM takes place after SM but happens with mostly the same events, and when you go back to SM Alola through the ultra wormhole, time has passed with Lillie back from Kanto, gyms have been built and so on so forth. Only reason imo they even confirmed a mirror Alola, to tease the dual world feature of USUM and confirm an AU story that works as a continuation.