start a new game and then instead of doing a normal mission, the other type of missions

What do you mean the rest of it? If you want more, get all ten endings (beat hero and dark
missions for all of the sixth stages), and you will unlock the Last Story. in this, you
can fight Devil Doom as Hyper Shadow, and when you beat him, you unlock the Shadow Rifle,
which is the most powerful weapon in the game. This weapon makes it easier to kill the
alien tank, the president's craft, and eggman's balloon. Congrats, you beat the game. Oh,
and get all A rankings. You unlock Super-Hard Mode.