Unlock Secrets
As you progress through the game you will earn fighting points. These points go towards unlocking secrets in the game itself. If you want to unlock everything you will need 2000 points. Here is the order that the secrets are unlocked:

Extra Lives: This allows you to have 9 lives.

Stage Select: You can choose from level 1 to level 6.

Color Change: Changes character color and unlocks Alpha Guy and Alpha Cody.

Rapid Punch: Now you can simply hold the punch button and you will punch rapidly.