This Challenge Hall is a place that seems empty often throughout the game, so it's easy to miss when it is relevant. There are several times during your journey that it will open with a tournament called the Challenge Cup. Be aware that if you earn a medal while the Challenge Cup is going on, it will end.
- After you earn 3 medals. Rewards you with Mewtwo PR12.
- After you earn 5 medals. Rewards you with Mew PR14.
- Once you've defeated the Grand Masters in the Pokémon Dome. Rewards you with Arcanine PR01 - this is also available in a trade at the Water Club.
After these set events the Challenge Cup will also randomly be going on when you start up your game.
The Challenge Cup is a tournament where you face 3 opponents in a row, and if you beat all 3 you earn your self a promotional card. However, if you lose to even one of them, you'll lose the cup and not get anything. You can save between duels though, so this shouldn't be a problem. Your first two opponents will be randomly selected from the club members of each of the clubs. Your final opponent for the Challenge Cups based on having medals is always Ronald. He'll be using his Invincible Ronald Deck.
The challenge cups that appear randomly will reward you with a random promotional card as well. This does not include the phantom Mew or Venusaur cards though.