>>37122748Short answer is "everything", although for the sake of discussion and community understanding, there is certain stuff that is generally considered retconned out when remakes make a distinct alteration or change that isn't simply due to version differences or multiverse shit.
Old typings like Magnemite being pure Electric type for example, is retconned information. Or Green not being canon, which was due to the fact that she was non-existant as an NPC and it was explicitly clear that Red was the canon protagonist of Gen 1.
Then LGPE basically reverse-retconned that, by showing that despite Red being a constant source of continuity in the timeline due to his many aged appearances, it can still be canon that alternate versions of events with different characters can happen, and that despite Red's existence, Green does in fact exist too.
Honestly though, it doesn't matter too much. Pokemon does have a canon/continuity that can be abided too, but Game Freak aren't shy to make retcons and alterations, and being a kids series its probably never going to get too deep. Canon rarely matters more than game-to-game or beyond two Gens at a time. Whenever games are more than 2 Gens apart, there will usually be some kind of retcon to crop up, like type changes, character replacements, ambiguous timeskips, ect.
It can be kind of interesting to follow for an autist like me, but I think most people jumped ship and stopped caring after OR/AS made such a big deal about the multiverse. Even though it technically didn't alter the continuity or timeline anymore than X/Y already had, it rubbed people the wrong way and made people stop caring because GF made it seem like nothing mattered and anything could be brushed aside as a multiverse thing.
And to be fair, they have done that all throughout Gen 7. We got SM, and then both USUM and LGPE were "alternate universe!" versions of their previous games. But we got Green confirmed out of it, so I guess it's not too bad.
