If you could have any combination of features patched into a mainline generation, with that patch becoming canon to all copies of those games every produced, what would it be? Can be anything from the PSS to a single shiny sprite being fixed to Gen 1 being bug-free.
Starting with a narrow range to keep discussion from devolving to dexcut memes. Will make a few more broken-up gen threads if this one is successful.
I'd add following Pokemon and the PSS to Gen 3 - Gen 1 and 2 keep large chunks of their character from their underdeveloped stats systems and borderline beta features.