Fight as Goro
Complete the game. Hold Up Left A Select when the phrase "The End=" appears after the credits. Continue to hold the buttons until the initials entry screen appears. Enter your initials and press A the press Start at the high score screen. The message "Goro Lives=" will confirm correct code entry. When fighting as Goro hold A B and press Down. Goro will disappear and the match timer will count down quicker. Additionally your opponent will cycle through the same move and will not be able to hit you.
Fight as Smoke
At the Title screen press Up Up Left Right A B A B Up Down Up.