Complete the game in extra mode under the normal or higher difficulty level. Then, press Down at the plane selection screen to access the black proto fighter.
Difficulty select
Press B, C(2), B, C(2), B, C(2), then hold L and press C(2) at the title screen.
Secret Jets
Beat Extra Mode as every available jet. Doing so will unlock that jet's alternate make for every mode of game-play. Press DOWN during the Select Fighter screen to access the secret jets.
