Secret Act 1

Get an ‘A’ or better rank on all twelve acts to unlock Secret Act 1.

Secret Act 2

Successfully complete Secret Act 1 to unlock Secret Act 2.

Alternate costumes

While choosing a character at the character selection screen, hold L + R.

Bonus characters

Successfully complete the indicated task to unlock the corresponding character:

Chi-Chi: Successfully complete Story mode.
Fu Lum: Successfully complete Story mode.
Mai: Successfully complete Story mode.
Neo Piccolo: Successfully complete Secret Act 2.
Oozaru: Successfully complete Story mode.
Piccolo: Successfully complete Story mode.