Play as Reiji
To play as the final boss, press A, B, Right, Left, Right, Left, Down, Down, up, Up at the title screen.
Play as Gourki
To play as the sub-boss, press Up, Up, Down, Down, Left, Right, Left, Right, B, A at the title screen.
New Bodies for Create-a-Character
Create a character and proceed to train it. Keep training until you have 90 moves for that Character. Now go and create a new character. There will be two new bodies to choose from; one male and one female.
When you get knocked down, keep on pressing any of the c-buttons and you'll get about two hits worth of health.
Before selecting your player, hold the L button and press left or right on the digital pad. The rotating character pictures will change color indicating the trick worked. Keep holding L when you select your character.