Press the L button on the main menu to reveal the words "Dragon Click" on the Dragon Rader. Press R to start the game, which simply requires you to press the R button as many times as possible within the time limit.
Card Sheet Unlocks
In order to unlock Card Sheets 13-17, just complete chapters 1-5 with a Z rank on each. In order to get a Z rank, you'll have to minimize the damage you receive and finish fights as quickly as possible.
Janemba - Finish Story Mode
Vegeto and Gogeta - Finish the final chapter, taking the top path will give you Vegeto and the bottom path will give you Gogeta.
Adult Gohan Super Saiyan 2 - Beat Broly in Chapter 2-6
Adult Gohan - Super Saiyan - Beat Frieza in Chapter 1-8
Cell Super Perfect - Beat Cell in Chapter 2-5
Goku Kaioken - Beat Krillin in Chapter 1-2
Goku Super Saiyan 2 - Beat Fake Goku in Chapter 2-2
Goku Super Saiyan - Beat Janemba in Chapter 1-9
Gotenks - Beat Gotenks in Chapter 1-4
Gotenks Super Saiyan - Beat Gotenks in Chapter 1-5
Piccolo Fuse with Kami - Beat Cell in Chapter 2-1
Pikkon - Beat Janemba in Chapter 2-9
Vegeta Super Saiyan 2 - Beat Janemba in Chapter 2-7
Vegeta Super Saiyan - Beat #18 in Chapter 2-3
Finish Dragon Road, go to the main menu, and press L on the Dragon Radar. Dragon Player will appear. Selecting it allows you to listen to the music from the game.