>Lake Guardians
Legends: Arceus gave Uxie, Mesprit, and Azelf a nice new signature move in the form of Mystical Power, but that is not much compared to the other Sub-Legendary groups. Regional Forms or Convergent Species would both feel very out of place given the trio's established story. An additional member would also be too strange, since the Lake Guardians, alongside the Creation Trio, form a complete sextet that collectively are the offspring of Arceus. Personally, I think "Therian"-style form changes would be fantastic for the trio. Label them "Origin" to indicate that these three Pokemon are also seeking or channeling power from Creator Arceus in order to manifest these new visages, as well as to provide another link between them and the three dragons. Furthermore, it would provide Uxie, Mesprit, and Azelf with a much needed visual update. Maybe even add a new typing to each?
>Guardians of Alola
Tough call. They share a signature move, and each has a powerful Ability. All of them have designs that are consistent amongst each other, but are differentiated more so than the Incarnate Forces of Nature or the Lake Guardians. The quartet are very reflective of the region from which they hail, so adding additional members or foreign forms might also be strange. Paradoxes will likely stop being designed or developed after The Indigo Disk releases, so I doubt they would be eligible for any at this point in time. Like I said, I cannot figure out what to do for them! Game Freak might have actually done a sound job with the Tapu Quartet lol.
>Eon Duo
For Latias and Latios, I could easily see Legendary Wings-style Regional Forms or Convergent Species being done. Powerful Legendary Pokemon that are so painfully similar to Latias and Latios, yet share little to no connection with the Hoennian Legends.
