>>57973406i'd say compatibility are the best way to define timelines.
Time Machine era [No natures or abilities]
RBY -> GSC
PNC/GTS era [Contest/Musical Timeline. Has Sevii islands.]
RSE-FRLG (creating the PNC link) -> DPPl-HGSS (red gyarados as cryptid on tv) -> BW -> BW2
Bank/Home era [Mega/Fairy Type Timeline]
XY-ORAS-LGPE(???. Red has already beaten the league. But did not foil Rocket's plot to steal the one and only masterball prototype, that's Chase. But it has to still be early on in the timeline because the other two games have masterballs. But also there are megas, which had only been very recently discovered in XY, because Sycamore thinks it only happens in Kalos? It's possible LGPE is simply in its own timeline or noncanon entirely.)-> USUM (red is like 30, still has megas)
Mega timeline is guaranteed a separate timeline from GTS, not only because of the whole Zinnia thing, but also Rainbow Rocket versions of gen 3 evil team leaders look like their GTS era counterparts, NOT their ORAS version. There are at minimum 2 versions of Maxie and Archie running around the multiverse, even if you assume the entire GTS timeline is a doomed timeline where the heroes never win, which is unfounded, especially because Cyrus winning precludes Ghetsis and Lysandre winning. It might almost be better to talk about these like timeline clusters, or alphas and offshoots. Rainbow Rocket's leaders were from the same cluster as GTS era, presumably doomed offshoots.
Presumably SWSH and SV are mega timeline? There's no megas or z moves mentioned. It's possible they exist in one of the other two I suppose.
Similarly, PLA and BDSP clearly have some kind of timeline connection between them, because they have lore interaction. But I don't know where they fit in any of the 3, if not perhaps even their own because PLA involves time travel. They are now home compatible, but both weren't for the longest time. Also Go is home compatible as are VC gen 1 & 2 so not the best litmus test.
