Unused Graphics

There's not a spectacular amount of unused content in Metal Slug 2 - a lot of the tiles are merely leftovers from the previous instalment.
A general note: the graphics in Metal Slug 2 are very strangely organised. Player graphics are strewn all over the place and arranged in contradictory manners - sometimes graphics for Tarma and Eri are in the same "full" assembled manner as they are in later games, while at some points they're kept as "headswap" tiles, where only the relevant chunks are stored to be applied to Marco or Fio's graphics. Because of this, some animations are repeated multiple times through the graphic data. I can't really keep track of everything.

Source: 4597

Not unused, just obscured: the staircase on the left is off-screen by the time you destroy the cannons in Mission 1. Cheers to The Huntress for this find.

Source: 128633

The cannon towers in Mission 1 have animations for their curtains being drawn. Cheers to The Huntress for this find.

Source: 75485

Not unused but merely unseen, the destroyed bus in Mission 4 has this rough outline hidden behind a layer of rubble. The text reads "優先低"; roughly "low priority" or "bottom layer".

Source: 80348

Right at the start of Mission 6 is a tower with a searchlight on top. These unused graphics suggests the tower was destructible at one point, but it can't be interacted with. Ta to Division 六 for the find!

Source: 99060

Ivo found the cat and esreveR ripped it. I've no idea where you'd see the cute little thing, though it is depicted in the concept art, and still exists in the data as a functioning object.

Source: 100259

This monkey is stored with the new item graphics (such as the pig, Hyakutaro's fireball, etc) and has animations for walking, jumping, and smash its fists together; these are remnants of unused behaviour that would cause it to seek and destroy points items! The monkey item found in-game just sits still.

Source: 100867

Each of the animal Slugs have two different win icons: One of them standing, one of them sitting. The sitting Camel Slug one is used, but not the standing one. Left over in Metal Slug X.

Source: 110589,111975

The Eaca-B's sprites were updated for this game, boasting lots of new frames of animation for its aerial rotations, and even applying those luxuries to the propellers and Flying Tara's bomb. Unfortunately, the Rebel planes no longer perform loop-de-loops after the first Metal Slug, so all this work was for naught. Credit to The Huntress for this observation, whose sprite sheet shows all the relevant frames.

Source: 106519

Fio using Eri's win animation. Given the use of "headswap" tiles, this was probably made as a base for Eri later, perhaps.

Source: 113179

Abul Abbas wringing his sword mournfully. Presumably he would do this before waving his surrender flag.

Source: 113365

Abul Abbas stabbing with his sword. This is stored at the end of his walking animation, and it appears to flow smoothly in and out of it. As it is, the only time he's walking is when he's escaping off-screen, but unused code would have him attempt to backstab players when they're not looking!
These two animations later saw use in Metal Slug Defense. Thanks to The Spriterminator for the tip.

Source: 115215

Divison 六 found these frames suggesting the Ajirabian soldiers could've performed a crouching stab, possibly after somersaulting. According to SoldierRebel they will actually use this animation when the difficulty is set to 8 while somersaulting out of the Keesi, but I've yet to see it myself.

source: 116473

Another Divison 六 find of the Ajirabian soldier seemingly climbing off the camel (it's found in the proximity of other camel-riding animations).

Source: 139358

This is apparently the Aeshi Nero/Mission 2 boss's laser thinning out. But, uh, yeah, I can't understand a lick of these tiles. Thanks esreveR?

Source: 149156 (Fio)

Source: 187763 (Tarma)

Source: 190131 (Marco)

Source: 193996 (Eri)

Unused frames of the fatties looking upwards and turning. This has been used in every game since, and not one of them has used the animation (though MSX did update it so the ladies have their proper legwear).

Source: 149291 (Fio, HMG)

Source: 149363 (Fio, pistol)

Fio and Eri turning and shooting upwards.

Source: 149383 (Fio, pistol)

Source: 164541 (Fio, HMG)

Unused looking up animations.

Source: 178195 (Fio)

Unused crouching and throwing animations, based off the same animations for Marco and Tarma from the first game.

Source: 152140

The Dragon Nosuke, the boss of Mission 3, has eight directions with unique idle and firing animations for its fireball-spitting cannon. Ta to Division 六 for the find!

Source: UNKNOWN

According to Ivo, this little scarab beetle is unused. Can't remember which games it's in. Also has a flying animation, thanks to Domino for pointing it out.

Source: UNKNOWN

esreveR pointed out to me that Mission 4's boss, Big Shiee, never has a flame trail on these animations. Yup.

Source: UNKNOWN

tango_311 found these in MS2 near the graphics of the bikers, presumably to be used as part of their debris, but they aren't used at all.

Source: UNKNOWN

This isn’t really an unused sprite, but you never get to see it properly, so I guess it goes here. It’s the animation the soldiers play when they kick down the doors of the carriages in Mission 3. Found by Ivo, in both MSX and MS2.

Here's an incomplete list of leftovers from the first game.