When you get inside, you'll be in Gotham. Click on Batman to play a mini-game. The objective of this mini-game is to dodge balloons and catch the Joker.
Once you complete the mini-game, you get two prizes. You get a Grappling Hook, which is a cutscene of Batman swinging across the screen, and a Bataring, which is an item you can throw.
If you are having trouble with the mini-game, below is a video tutorial of it!
Until next post everybody.