Expert Mode: On the 'How to Play' screen, enter <- , -> , <- , -> , wait for 1sec, then -> , <- , -> , <- . If you did it correctly, 'EXPERT' word appears on the bottom.
Speedup Mode: At the character selection screen, hold START when you're choosing your fighter.
Small Characters: (only works with VS mode) When you pick up your character, hold B+C on both sticks during all the time before the fight starts. You have to do this before every fight if you want it to work each time.
Hidden Characters: Save after beating Jin ChonRei. Then load the saved game and start a new game. At the character selection screen, press B when highlighting fighters in this right order: Terry, Hon Fu, Mai, Geese, Bob, Sokaku, Andy, Bash, Joe, Mary. A sound will inform you that the tip worked.