Completion bonuses: Successfully complete Story mode as Marco to unlock
the Monolith with unlimited ammunition and the Extras menu (with
"Mini Game", "Color Edit", "BGM Test",
and "Movies" options).
Laboratory staff: Collect the CDs hidden in the various locations in
every mission. Then, enter the "Garage" screen and select
"Laboratory". The staff will be found inside.
Slug Gunner: Add the Gunner Core, Gunner Arm, Gunner Cannon, and
Gunner Leg to Metal Slug in the Slug Laboratory.