You are in the world coronation series tournament in the tournament it’s you, Ash, Leon, Iris, Cynthia, Diantha, Lance, and Raihan. The first battles are Ash vs Iris, Leon vs Raihan, you vs Cynthia, and Diantha vs Lance.

before you go to fight Cynthia (which you fought before and won) you and Ash wished each other luck for each other battles

later your battle with Cynthia starts and the Rotom commentator says you can use up to 3 Pokémon and use 1 Mega or Gigamax