Walkthrough: Since leaving The Alola Region to train in Kanto and Johto, Gladion will occasionally return to challenge the Pokemon League a month after you first defeated Necrozma. He will look to put forward what he has learned since your last battle with each other, having the advantage with your Starter Pokemon once again with his varying Silvally.
Pokemon Trainer Gladion (Rowlet Starter) - Level 68 Crobat, Level 68 Zoroark (Darkinium Z), Level 68 Porygon-Z, Level 68 Lucario, Level 68 Venusaur, Level 70 Silvally (Fire Memory)
Pokemon Trainer Gladion (Litten Starter) - Level 68 Crobat, Level 68 Zoroark (Darkinium Z), Level 68 Porygon-Z, Level 68 Lucario, Level 68 Charizard, Level 70 Silvally (Water Memory)
Pokemon Trainer Gladion (Popplio Starter) - Level 68 Crobat, Level 68 Zoroark (Darkinium Z), Level 68 Porygon-Z, Level 68 Lucario, Level 68 Blastoise, Level 70 Silvally (Grass Memory)