Well, Marnie would still have her Grimmsnarl, Luka's gonna have an Orbeetle, & Fantina will Gigantamax her Gengar, despite her ace normally being Mismagius. the Final Boss will have a phase where he will Dynamax his Galarian Articuno.
For Mega Evolution, Jasmine will Mega Evolve her Steelix, Korrina will have more Pokemon on her team than she does in X & Y (This will include Mega Lucario), Jacinthe will still have her Mega Clefable & the Final Boss's Mega Evolution phase will involve Mega Floette
For Z Moves, Erika will have her Vileplume use the Grass Z Move, Lana will Either use the Water Z Move for her Primarina, or it's exclusive Z Move, Pico will use the Dragon Z Move with Archaludon, & the Final Boss Z Move Phase will involve Arceus using all of the different type Z Moves
For Terastalization, Winona will Terastalize her Peliper, Iono will Terastalize her Mismagius, Chill Penguin will have an Ice Tera Type Tyranitar that knows only Ice type Moves, & the Final Boss Stage with Terastalization will have his Poliwrath with a special Tera Form
Post Game all the Gym Leaders & Elite 4 Menbers will have Legendary/Mythical Pokemon in their rematches