Knife Edge: Nose Gunner
At the Kemco logo screen, hold L + R +C-Up, then press C-Right, C-Left, B . The "Super Hard" difficulty setting may now be selected.
Select "Story" or "Team" mode, then hold C-Left + C-Right + C-Up + C-Down + R and press Right, Up, Left, Down when the level number is displayed.
Thanks to Revolution reader Qu9inn!