Highlight the "Exit" selection and press A + B + C + D at the options menu. Alternately, select Japan as the country on the options screen and exit the menu. Immediately re-enter the options screen and select USA as the country.
Fight as Kuroko
Select versus mode. Press Up, Down, Left, Up, Down, Right + A.
Haohmaru: Defeating EarthQuake
When the battle starts, jump forward to EarthQuake then immediately press Half Circle Back on the D-pad, Down, Forward, Back, Down, Back, B + C. Note: This only works 80% of the time.
Invincibility
Press A, B, A, Up, Down(2), C + D, Left.
Ukyo: Defeating Koruko
Press D during the battle, then press Down, A + B.
Unlimited "POW"
Press Start on controller one and highlight the "Options" selection. Press Start on controller two. The "POW" selection on the options menu may now be set to "Max".