Change the control settings:
Just pause your game and press and hold L + R + B + A.

Unlock Alpha Cody and Alpha Guy:
At the character selection screen, push Left or Right  to choose these fighters. Alpha Cody will be bigger and Alpha Guy will be stronger.

Unlock secrets:
During the game, you will slowly earn fighting points. These fighting points go towards unlocking secrets in the game. You'll need 2000 points (approx) to open everything up. Each level gives you about 50 to 100 points, ranging from the first to sixth level. The secrets opened up include: extra lives: up to 9 lives, Stage Select : 1 through 6, Color change for all characters: Also unlocks Alpha Guy and Alpha Cody as two new characters, and Rapid punch: which allows you to hold Attack to punch rapidly.

Get extra gems and items:
Turn your back to rolling barrels, quickly turn around and hit it using your special attack. After you break the barrel extra gems or other vital items will fall out. Remember that all barrels don't contain gems and items.

Restore your life bar with healthy dog - Stage 5:
Midway into the stage (after you leave the bad bathrooms) you should see a dog. If you get close to this dog  and walk up and down from him, then you will recuperate your life back.