>>29942497ok so first of all, some Pokémon are region locked. If you look at the Alolan dex, we mostly got old-gen Pokémon that can either fly or swim over the sea or that get to the island via human transit in boats or planes.
So, no Lunatone and Solrock, unfortunately.
To have a game where there is every single mon available, you'd have to have at least 3 regions, in my opinion.
On top of that, have something like the trophy garden in DPP. Some rich guy who actively imports Pokémon to his yard.
If you befriend him by doing quests, he allows you to roam the garden and catch whatever you like.
Each week, there will be a set of 15 or so different Pokémon you can find.
On top of that, maybe have a harbour. Once every month you have a huge cargo cruiser landing. On board there's items to be found and battles to be had. Maybe make it randomized, maybe actually patch it in everytime like a small DLC. With the sailing ballast water and on board as well as clung to the ship's keel you also get foreign Pokémon, say Staryu and Clamperl. You also might find the Deep Sea Items here.
I think stuff like that would be a good idea to enrich the region so that you can actually end up catching them all without some intergeneration trading hocuspocus which is always breaking the character of the game.