Place your cursor at the field with the question mark while you enter the
cheats!

BISON

Push L while you enter 2x left, 2x down,  left, 2x down and X+Y.

AKUMA (GOUKI)

Push L while you enter 3x left, 3x down and X+Y.

DAN

Push L and R while you enter Y, X, A, B, Y.