Hint: Change the Time on the Clock:
To change the time on the clock in the clock level, simply change the console's system time.

Hint: Cheaper Extra Fighters:
Exit and re-enter the shop screen until the price of the extra fighters are lower.

Hint: Multiple Character Selection:
You must unlock every costume and character to choose multiple people (i.e. you can choose clones of the same person, even for both players).