What better way to start off a series than by having a heap of unused crap lurking inside? Findings are sorted by whatever graphic comes first in the tile viewer.
Props goes to Ivo, V-King, tango_311, stoffhime1 and Magma Dragoon for finding a lot of this stuff.
Not even Metal Slug escaped from William S. Sessons' campaign of drug awareness! ... except it goes entirely unused and isn't seen in-game at all. Whoops!
This cute little Slug turret is found at the end of the menu alphabet, and actually dates to a prototype of the game where you only played as the tank - see early footage for details!
And I can't find the right palette for this (it's meant to fade from yellow to red), but this is a health bar from the aforementioned early revision.
S, G, H and M icons. Placeholders or early HUD icons for the weapons, presumably.
A large, rotating Nazca Corporation logo (you'll have to take my word for it on the rotating part! check out Magma MK-II's sprite sheet for the full thing). The developers looked like they'd planned to make it clear as mud who was responsible for the game, but it goes unused.
A jingle and soundbyte for this alleged screen can be heard in the sound test at 2C; it was also included as the first track of the Metal Slug Complete Box soundtrack - thanks to Stefano for this factoid!
Animations for the dogs from Mission 5 walking and sniffing, found by Ivo. You only ever see the dogs running in-game, though the early footage appears to show one of these animations in action.
A little otter poking its head up from the water, found by Ivo. Might be used somewhere for all I know.
Ivo found these barrels in the vicinity of Mission 2's graphics. Are they used anywhere?
Division 六 found these unused frames from Morden's sprites in the 2-player ending; these would make a better transition from his idle stance to him seeing the paper plane, but instead he just cuts between two different poses.
An elk. Presumably for use in Mission 3 or the ending movie scenes.
It appears in the Metal Slug Official Guide Book character chart, representing the decimated wildlife that have it out for Morden.
A very peculiar sprite of an enemy soldier with a distinct uniform. No one seems to have found a fitting palette for it that colours the mouth and eye (visor?) correctly. This is the only animation it has, though there are copies of it rotated in around 10 directions. Ivo suggests it might be the character depicted in this concept art. It's possible!
Divison 六 suggests it may have been the Metal Slug pilot from before Marco and Tarma were introduced; the sprite fits perfectly into the chassis during the Slug's "damaged" animation, and the multiple rotations fit with how many directions the tank can face. It's possible too!
This stupid kid has appeared in all of the games' data, but not actually in gameplay. tango_311 provided the real palette.
These three ladies only have one frame of animation each, and it goes without saying they're unused or else they wouldn't be on this page. They have no animation, implying they would have only been used for the ending sequence.
The Metal Slug's tiles are arranged strangely so this animation is a bit splotchy, but it appears to be firing its cannon while crouched; using the bomb button while ducking will just throw a grenade. This appears to be a leftover from the early development when the Metal Slug was the only playable character; early footage suggests crouching and using the cannon would have fired a different projectile!
The game is already dripping in rotated sprites... but I can't think of a purpose for these tilted splashes. There's a watery slope in Mission 1 but it just produces regular hitsparks, not splashes.
What appears to be a cargo lift, probably for the Metal Slug or enemy tanks. Found by Ivo. Not sure what it woudld be supported on - a helicopter? A crane?
The Metal Slug's vulcan cannon detached and sparking on the ground. One can assume this would happen after the tank is destroyed, but it explodes in mid-air no matter what.
The Metal Slug has ludicrous amounts of rotations - more than are actually feasible in-game! This is but one example, there's way more than I could possibly cover. Thanks to Ivo for this trivia.
In the game's early development, ally soldiers would have thrown pipe bombs rather than the enemies' psychedelic flashing pineapples. That feature was dropped and the pipebombs given to Marco and Tarma. Notably, there's an animation for a soldier running while throwing that was never modified for the enemies' grenades, a clear leftover from the game's original design.
Despite being unused, these sprites have been carried across to other games, and even appeared in promo materials like Metal Slug 3's manual!
A soldier exposing his tongue and plugging his ears. A taunt, or a reaction to an incoming enemy attack? Thanks to Divison 六 for pointing this out.
This animation later worked its way into Metal Slug Defense and Attack... as part of the soldiers' diving animation, for some reason.
A variant of the knifing animation with the soldier snarling happily. I almost think it's used, but we all know how many times I've been wrong.
This was later reused for a Rebel variant in Metal Slug Attack.
The soldiers in floaties have animations for aiming and shooting diagonally, but they never do it! That's either very kind of them or very foolish. Cheers to Divison 六 for this find.
Located right before the graphics for the Melty Honey. The driver actually loads these shells during the reload animation (
), but fires the far larger homing missiles; likely replaced for the sake of visual clarity. Cheers to Divison 六 for this find.
An entirely unused tank is hidden inside the game! Its style is very reminiscent of In The Hunt and Gunforce 2, games made by Irem that apparently was made by the Metal Slug staff before moving over to Nazca.
Named the "KT-21" in concept art, Ivo believes it was an early version of the Di-Kokka (the rounded fat tanks) - its animations hit all the same beats, from its recoil-heavy fire, its wobbly movemeent, and its hatch opening when it's destroyed. The Di-Kokka even has an unused tank shell very similar to the one above, if you read on!
In the game's early development there were no hairy POWs, but instead captive soldiers! See early footage for more on their behaviour. Though these GIFs use their usual palette, their uniforms would have been blue and changed hue depending on which player rescued them. This probably explains why the ending in 2-Player mode has the soldiers dancing and celebrating in the streets, despite the fact they were defeated.
These were later used in the console ports of Metal Slug and Metal Slug 3, Metal Slug Defense and Attack's menus, and were modified for the trainee soldiers in Metal Slug Advance.
An unused shell found between the tiles for the Girida-O and the Iron Iso; it's possible they used this missile instead of cannonballs. I believe these remain unused in Metal Slug 2 and X.
The Iron Iso turning around. It's possible it would play this in-game, but the camera never gives you the chance to get behind it - not until Metal Slug 4, at least. Cheers to Division 六.
Located after the Iron Iso's destroyed animations are these frames of its turret separated from its chassis.
Early footage suggests when destroyed its turret would have popped off, similar to the Girida-O.
Found after the Iron Iso's graphics are these trailed projectiles... and immediately after them, the orbs the Iron Iso uses in-game for its projectiles.
A sandbag with a wider, shorter profile. Not unused, just stupefyingly obscure - it's found inside the shack at the beginning of Mission 4! It's fully functional and only became visible to me in the first test stage. Thanks to Ivo for pointing the object out to me, and Division 六 for its appearance in Mission 4!
The Bull Chan only stops in one direction, but three additional variations of the stopping animations are unused, where the tank is seen already facing other directions. Credit goes to Division 六.
This animation is used but rarely seen - in 2-player mode you can backtrack slightly with the Metal Slug and see this animation when the rock trap lands on it. Cheers to ZeroTheEro for this factoid!
The Flying Tara (and Eaca-B) with a missile or bomb as part of its sprite. In-game, the missile or bomb is a separate sprite overlaid by the plane, likely to facilitate its flashing palette. Cheers to The Huntress for this observation.
The turret outposts in Mission 4 have four unused variants with varying cannon ports and amounts of foliage. The top-left design would later be edited for use in the second mission of Metal Slug 4. Cheers to Division 六 for the find!
What we have here is a Rebel soldier using a turret. Although they do use missile turrets in Mission 5, they don't use the same turrets you use in Mission 6. Has all the necessary animation, too!
Curiously, Marco and Tarma's turret animations immediately follow these sprites. All of their sprites are otherwise found at the very end of the sprite data in one organised lump.
A parachute Ivo suggested belonged to a Slug. If true, there really must haven been more emphasis on the 'chutes early in production, what with all those animations for Marco and Tarma while parachuting. There's more frames, of course, but he couldn't be bothering ripping them. Wise man.
A larger water splash for the Middleson boat seen in Mission 6. Cheers to Division 六.
An alternate set of unused turret graphics; it has only one ammo box, faces only four directions, and has no outline unlike the used sprite. These are seen in early footage of Mission 6, manned by ally soldiers and ejecting bullet casings as they fire... which, conveniently, are located right next to this in the tile data. Cheers to Division 六 for pointing the leftmost one located slightly later in the data.
An armoured car with a tank's entrance hatch and sandbags, falling. Judging from the sandbags, I'm assuming these were for the stronghold in Mission 3, but that's very little to judge off.
Ivo also made a second version with a palette that actually existed in the game, but it looks like ass in my view. Diss!
Ivo found this cannon shell near the Di-Kokka's graphics; early footage shows them firing these instead of their trademark fireballs. The fireballs are among the last sprites in the game's data, just before Marco and Tarma.
An incredibly elaborate explosion or dust cloud. Used in the tank-only prototypes for the Metal Slug's cannon explosions.
A dustcloud, probably kicked up by the Metal Slug. As far as I'm aware this visual effect doesn't exist in the first game (I thought I'd seen it...!), and later games use a less elaborate graphic.
Rolling balls with Roman numerals inside of them? It's possible these were alternate projectiles for the Metal Slug, based off some early footage, though I'm not 100%. They are used as part of the debug dipswitches to keep track of how the Metal Slug and other tanks balance themselves on sloped terrain... but a single static frame is used, with none of the rolling animations.
Seemingly an early animation for the shotgun blast.
Found among the Metal Slug's tilted cannon blast animations. Intended for the Metal Slug's rolling projectile from the early prototypes, perhaps?
Found near the graphics for the Hairbuster Riberts (Mission 2 boss); an exhaust intended for the missiles, but goes unused. Cheers to Divison 六 for this find.
Unused gun emplacements. The left one is static, but the latter can face in five downward directions. Ivo and Dave found these in the vicinity of Mission 1's boss graphics...
... and early footage shows they originally placed on the wings and shot at the players - or could be hijacked by friendly NPCs! See unseen objects for their in-game properties.
Alternate crouch throwing animations for Marco and Tarma. These animations have lasted up to Metal Slug 5, and even Fio and and Eri were given similar animations in their debut... but not once are they ever used.
 
 
  
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Ivo found animations of the characters shooting and throwing things in many directions while in the air, but I got these and animated them. It appears that the characters would've been more flexible, turning from every angle, instead of just turning their whole body around to whatever direction.
What's interesting is that just about all of these animations are still in the game! When your character parachutes in (in Missions 1, 2 and 6), release them from the parachute, aim left, and fire. Throwing grenades also works, and the Combat School in the console ports allows the machine gun wielding animations to be used thanks to you keeping your weapon after finishing a level. Thanks to V-King for most of this info.
These turning animations, however, cannot be seen in-game.
Some of these animations were modified and repurposed for the unused helper character in Metal Slug 5... who also went unused, you might have gathered. They finally appeared somewhat as intended as the Special Marco unit in Metal Slug Attack.
Alternate aiming upwards?
Unused graphics for looking up and turning while shooting.
This cartoony grenade-juggling monkey lurks among the HUD and the text, and appears there in just about every instalment (at least, I'm sure it used to - have newer ROM dumps excised it?). It's used on the loading screens of the original console ports of the first two games.
