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Indigo Disk might hint at the Water-type starter, which is a pretty safe bet anyway. By the time of the Meiji Restoration, shinobi had become a topic of popular imagination and mystery in Japan. Ninja figured prominently in legend and folklore, where they were associated with legendary abilities such as invisibility, walking on water and control over natural elements.
Tohjoan variants: Serperior (Grass/Steel), Incineroar (Fire/Poison), Greninja (Water/Psychic)
Evolutions: Weepinbell (Grass/Fighting), Arbok (Poison/Dragon), Hypno (Psychic/Dark), Ariados (Bug/Ghost), Ledian (Bug/Fighting), Sudowoodo (Rock/Grass)
Past variants: Meganium (Grass/Water), Raichu (Electric/Dark), Volbeat+Illumise (Bug/Electric), Golden Celebi (Grass/Flying)
Future variants: Feraligatr (Water/Fire), Sunflora (Grass/Fire), Absol (Dark/Poison), Silvery Celebi (Psychic/Poison)
Special: Unown (Collective Forme with another "all types" gimmick)
New: Predecessor of the beast trio (not the Eeveelutions, maybe Steel-type as in Brass), essentially a fourth member
That's 19. You could add up to a dozen if "era variants" for other generations, with the idea being that these are really Pokemon that traveled from other eras (not weird timelines). In the past era, humans don't yet exist. In the future era, humanity has been wiped out and Pokemon have to readjust. There is no robot shenanigans... If anything, future Pokemon have to fight the robots left by humans. Global warming (already acknowledged in SwSh) and pollution characterize this era.
If the PLA template isn't sacred (it shouldn't be), I'd like a revival of some of the Spaceworld Pokemon. I already sneaked two lost evolutions into my list, although I had to make Gorochu a future form for obvious reasons. If I could pick six more, it would be the Kotora, Norowara and Wolfman lines.