Missing Areas

There hasn't been any evidence of a debug menu in the game as of this writing, so it's tough to say how many unused areas there are and what purposes they served (most of them appear to be leftovers that would be finished up for Metal Slug XX), and it's a nuisance to access them! You could use Cheat Engine to level warp yourself, or you could use these DeSmuME savestates (13MB zip!).
(if anyone has the know-how to make more convenient cheats out of these, go right ahead!)

There are two values related to each area; those in address 033E4338 increase by 52 per area and load the background and mini-map graphics, while address 033E43E4 increases by 1 per area and loads the appropriate objects, enemies and collision detection.
... at least, I think that's how it works?
If you use the savestates you should find the addresses no problem, but otherwise your best bet is going to an area below and searching for the relevant values if the addresses are tough to find.

The area will load once you enter a new screen. Some stages load improperly from the mission select screen, though transitioning from one area to the next gets clean results.




Mission 1

358459840Mission start. Junkyard.
358460361Inside the junk.
358460882Tanks and junk.
358467123After boss cinematic.

Mission 2
358465044Mission start. Lifts.
358466086Sloped track with Slug Trolley.

Mission 3

358468168Mission start. Horizontal lift.
358468689Vertical lift.
3584692010Rolling ball.
3584702412UNUSED. Vertical junk tunnel.

Mission 4
3584712813Mission start. Cliffside.
3584718014Descending the cliff.
3584723215Man-eating plants.
3584733617Boss defeated.

Mission 5
3584785618Mission start. Parachuting in.
3584790819Descending the ruins.
3584796020UNUSED. Vertical junk tunnel?
3584801221Sloped path with laser cameras.
3584811623UNUSED. Small tunnel.
3584816824UNUSED. Underwater tunnel?
3584822025UNUSED. Same tunnel with soldiers.

Mission 6
3584744027Mission start. Snowy path.
3584749228Cliff ascent with future soldiers.
3584754429Uphill climb with sliding logs.
3584759630Entering the Slug Gigant.
3584764831Slug Gigant attack.
3584770032UNUSED. Black screen with Slug Gigant.

Mission 7
3584624434Mission start. Entering the base.
3584629635Inside the base.
3584634836Climbing the gauntlet.

Combat School (Mission 1)
3584837638Special Training A (avoid falling blocks)
3584842839Special Training B (destroy obstacles)
3584848040Special Training C (collect items)

Combat School (Mission 2)
3584853241Special Training A (destroy the air forces)
3584858442Special Training B (bounce the ball)
3584863643Special Training C (transport the ball)
3584868844Special Training D (collect the balls)

Combat School (Mission 3)
3584874045Special Training A (bounce the ball)
3584879246Special Training B (move the lift)
3584884447Special Training C (defeat all enemies)
3584889648Special Training D (enemy time attack)

Combat School (Mission 4)
3584894849Special Training A (collect items)
3584900050UNUSED. Scrolling background?
3584905251Special Training B (collect the balls)
3584910452Special Training C (defeat all enemies)

Combat School (Mission 5)
3584915653Special Training A (enemy time attack)
3584920854Special Training B (bounce the ball)
3584926055Special Training C (keep jumping)

Combat School (Mission 6)
3584931256Special Training A (Slug Gigant survival)
3584936457Special Training B (sinking snow survival)
3584941658Special Training C (sled chicken)
3584946859Special Training D (weaponless Slug Gigant survival)

Combat School (Mission 7)
3584952060Special Training A (platform time attack)
3584957261Special Training B (platform survival)
3584962462Special Training C (collect items on platforms)

35847024 / 12

A vertical passage made of junk, with paths and drops leading to the bottom. This area was made into an alternate path for Mission 1 in Metal Slug XX. This is the only unused area to have a functioning minimap and background music.

35847960 / 20

A vertical passage with a platform or two on the way down. XX made this into an alternate path for Mission 5 and greatly expanded upon it; it's possible all that is included here, just hidden off-screen. (don't suppose anyone knows what the addresses are for moving the camera...?)

35848116 / 23

A very short tunnel that the player enters from a gap in the ceiling; the screen stops scrolling once you reach an elevation. If you walk slowly then soldiers will spawn from behind. Another leftover Mission 5 alternate path for XX to finish up.

35848168 / 24

The same as the last area, only tinted blue (similar to its appearance in XX)... but most curiously of all, the player physics are slow and floaty as if underwater! The characters also only ever use their pistol graphics even if you're wielding a weapon, and a firing sound begins playing once you approach the elevation. Strange.

35848220 / 25

Same again, only there's a few soldiers along the way. The camera positioning seems botched, as soldiers will spawn from nowhere while on-screen and what looks like the edge of the map is visible from the entrance.

35847700 / 32

A screen with the player piloting the Slug Gigant. It appears to have no background, objects or collision detection of its own, and just loads whatever. The only things concrete about it are the Slug Gigant and that it only scrolls a tiny bit before progressing to the next area.

35849000 / 50

As far as I'm aware, there's no actual background, objects or collision detection attached to this area either. This is just a screen that causes whatever background is loaded to scroll downwards in a loop.