Walkthrough
Much like the Elite Four Members, your Rival will has improved his team immensely while your trainer was off completing the adventure in the Sevii Islands. All of his Pokemon are at much higher Levels since the last time you two met in battle, he even has replaced two of the Pokemon he used to have (Pidgeot & Rhydon) with even stronger Pokemon that are usually from the Johto Region (Heracross & Tyranitar) that you could have also found in the Sevii Islands. This Pokemon Team of his is the strongest in the whole game. Defeat your Rival this last time to complete the Post Game Story (and really the entire game as a whole outside of obtaining every last Pokemon in the National Pokedex)!
Rival (Bulbasaur Chosen): Level 72 Heracross, Level 73 Alakazam, Level 72 Tyranitar, Level 73 Exeggutor, Level 73 Gyarados, Level 75 Charizard
Rival (Charmander Chosen): Level 72 Heracross, Level 73 Alakazam, Level 72 Tyranitar, Level 73 Arcanine, Level 73 Exeggutor, Level 75 Blastoise
Rival (Squirtle Chosen): Level 72 Heracross, Level 73 Alakazam, Level 72 Tyranitar, Level 73 Gyarados, Level 73 Arcanine, Level 75 Venusaur