Champion: Pikachu, Lycanroc, Melmetal, Torracat, Naganadel, Rowlet
Elite Four: N/A
Frontier Brain: Sceptile, Pikachu, Snorlax, Charizard, Bulbasaur, Squirtle, Corphish, Swellow, Tauros, Grovyle, Heracross, Donphan
Pokémon League: Kingler, Muk, Pikachu, Lycanroc, Melmetal, Torracat, Rowlet, Naganadel, Snorlax, Charizard, Bulbasaur, Squirtle, Noctowl, Tauros, Heracross, Grovyle, Torkoal, Corpish, Lapras, Swellow, Glalie, Gliscor, Staraptor, Buizel, Torterra, Infernape, Gible, Bayleef, Goodra, Greninja, Hawlucha, Talonflame, Noivern
8th gym badge: Pikachu, Talonflame, Greninja, Snorlax, Charizard, Corphish, Grovyle, Swellow, Snorunt, Infernape
I haven't seen most of the unova episodes so can't add those pokémon.