Pokémon Trading Card Game/Ronald

Your rival in this game is named Ronald. You will meet him at various points in the game based on your progression. The first time you meet him will be when you enter the lobby of your first Pokémon Club. This is just his introduction though, there isn't a battle at this point.

Two Master Medals
After winning your second Master Medal, as you enter the lobby of the Pokémon Club you won it from, Ronald will appear and challenge you. He will be using his I'm Ronald Deck and winning will reward you with the Jigglypuff promotional card.

Five Master Medals
Once you win your fifth Master Medal you will once again run into Ronald as you're passing through the lobby to the exit. This deck will be the Powerful Ronald Deck and you'll receive the Super Energy Retrieval promotional card if you win.

Even More
There are more places you'll find Ronald as well such as the Challenge Hall.