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).
twifu udw, amdhiu.
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.