The villain team(s) are Team Evolve and Team Devolve.

Team Evolve is exclusive to Scarlet and Led by Professor Turo, Who believes that humanity and Pokemon are doomed to destroy themselves and each other due to their primal nature unless they find a way to force change upon them.

Team Devolve is exclusive to Violet and Led by Professor Sada, Who believes that humanity is doomed to destroy themselves and Pokemon due to humanity's overzealous desires for advancement and want to send the world back to the Stone Age.

The new gimmick is Primal and Advanced Evolutions(Basically the same as Mega evolutions),
Primal turns a Pokemon into a more primal and savage version of itself, and Advanced turns a Pokemon into a more refined and futuristic version of itself.

Notable Pokemon I know that have such forms are followed:
-Pikachu, Both, Electric/Rock (Caveman themed) and Electric/Steel (Cyborg, metal tail and a visor).
-Lucario, Advanced, Steel/Psychic
-Zoroark, Primal, Dark/Fighting
-Gengar, Advance, Ghost/Normal (Computer virus themed).
-Tyranitar, Both, Rock/Dark and Steel/Dark (Godzilla and Mechagodzilla themed).
-Coalossal, Advance, Steel/Flying (Sleeker, Wind powered themed).

New Eevee Evolutions, Rock and Steel, each exclusive their version.

Starters final Evolutions are:
Grass/Fighting, Tarzan Cat
Fire/Ground, Banana "Bull" Crocodile
Water/Ice, Bird Captain with Ice rapier

Legendary types are:
Dragon/Fighting and Dragon/Electric.
Third is a green two heads and represents Fate.