>National Dex returns
>Battle Frontier and contests return, contests are now an alternative win condition for the games (you still have to do the mandatory story beats but you can choose between gym battles or contests)
>speaking of mandatory story beats they're way less in your face. constrained to more of a grounded personal plot
>a well designed region with non-theme park like geography, either open world with actual things to explore or a recursive layout like Hoenn
>double battles are the standard format for big battles
>field moves are a thing again, each Pokemon can have two field moves at a time (which aren't tied to the actual battle moves)
>surfing, flying and riding Pokemon are all done by your actual party with visible model/animation changes instead of some shitty gadget or random tech legendary
>art direction based off Gen 2/3 Sugimori art
>online system from Gen 6 with open exploration with one other player (forces all battles to be doubles)
>no shiny lock
>old school events with their own unique locations
If I really had the freedom I'd probably redesign all the shit post-gen 6 mons that look ugly in a really blobbish simplified way and clash with older designs (looking at the dragon steel bridge thing and basically every starter since Alola that isn't Rowlett and the fire skull lizard) that being said that sort of thing is Pandora's Box imo, I would feel bad about taking away designs that people have grown attached to even if they personally suck in my opinion
Also I'd introduce either full blown open world remakes of the 'definitive' games every generation starting with FR/LG or the stereotypical all region MMO idea that everyone has. new mainline entries can be a testing ground of sorts that gets refined into these other games
Lastly bring back PMD, Ranger and random assorted non-mobile spinoff titles