Unlockables:

Dragon Power
After you have unlocked all the characters, set the difficulty to normal, and then choose Ultimate Battle. Select the practice option, beat ten enemies, and quit.

Miracle
After you have unlocked all the characters, set the difficulty to normal, and then choose Ultimate Battle. Select the practice option, and beat all 20 characters in a row, and quit.

Master Skills
After you have unlocked all the characters, set the difficulty to normal, and then choose Ultimate Battle. Select the practice option, fuse together the purple Potaras Miracle and Dragon Power.