Complete the game using any characters besides these three (Bolin&Polin, WiseDuck should be two of the three) or complete the game using all the characters. Go back to the techno dome and the 3rd minigame should be available.
Extra options
Beat the game in hero challenge mode with any character and in the end you will receive a certain amount of G You now have to go to Tatsumi's Techno Dome and move to the right You'll see several boxes in yellow. The ones in yellow you can buy, but first you have to withdraw G. You'll have several options such as more characters or hidden movies with the amount of G that you collect.
Mini games
To get a mini game complete the game with any character, after that go to an area where the secrets are unlocked.
If you complete the game with Dixen two times you will get a second mini game.