Hit the following buttons to get new fighters:
CIRCLE, RIGHT, TRIANGLE, UP, SQUARE, LEFT, CROSS, DOWN, CROSS, DOWN, SQUARE, LEFT, TRIANGLE, UP, CIRCLE, RIGHT, SELECT......This will give you GREAT MUTA if you SELECT the third character from the top on the fighter select screen
Power Warrior
SQUARE, CROSS, SQUARE, CROSS, CIRCLE, TRIANGLE, CIRCLE, TRIANGLE, UP, DOWN, LEFT, RIGHT, SELECT......This will give you POWER WARRIOR if you SELECT the seventh character from the top on the fighter select screen.