Unseen Objects

Big cheers to Mr_Beacon00 (信标先生) for working out a way to see these! His code replaces the first prisoner in area 2-02 of Mission 2 with whatever object ID is assigned. To see these for yourself, it requires the usage of Cheat Engine 6.83, VisualBoyAdvance 1.8.0, and this .CT address table.

To use:

If there are numbers under the Values column, success!
If not, double-click the Address of the cheats and confirm that the .EXE file under Pointer matches the .EXE at the top of Cheat Engine's window. If the Address is "VisualBoyAdvance.EXE" but the window says "VisualBoyAdvance 1.8.0.EXE", you'll have to add that "1.8.0" to it!

"Obj ID" is the core object, while "Obj Sub ID A", "B", etc., are modifiers that vary from object to object; some will change enemy behaviour, some determine what objects crates and prisoners are holding, movement speed, direction, and other properties.
For best results, use the "msa-us-objectswap.SGM" savestate and set all Sub IDs to 0.

Alternately, item and prisoner IDs can be modified using VisualBoyAdvance's built-in Memory Viewer. Memory addresses are inconsistent in Game Boy Advance games, but if you load the "msa-us-item spawn test.SGM" savestate, then the following should work. If you enter the following addresses in VisualBoyAdvance's memory viewer and change their values:

Once you destroy the hot spot, the changes will take effect.

ID: 7

It's the Slug Mariner! The unused vehicle intended for those unused underwater sequences and constantly teased in promotional art!
... and I can't figure out how you enter the fucking thing!
The quest to find this thing is just one tease after another, I swear to god.

ID: 90

The R-Shobu with an under-slung missile launcher. Common enough in the arcade games, but totally absent from this instalment! Its missile launcher has a tendency to overlap the helicopter, and its projectile is represented by... an entire Metal Slug. Graphical flubs aside, it appears to behave like it should.

ID: 92 ~ 95
item ID: FFFF

The ordinary bearded prisoner hides more than you'd think. By setting sub-ID D to FFFF (65535 in decimal) they don't drop an item when rescued, but instead be recruited as Hyakutaro! He will follow the player and launch homing fireballs when enemies are on-screen.
He's missing his melee attack, and his fireball has a few quirks - it only launches after his firing animation has finished, it launches from behind him instead of his fists. All that, and each fireball only does 10 units of damage, which is less than even your default handgun with the Handgun+ card equipped...!
Occasional graphics glitches can occur when Hyakutaro is present, perhaps a result of eating into the already-limited VRAM.

ID: 123, 124, 125, 126

A large wire fence. 123 is a taller one that has a hole torn in it when destroyed, 124 is shorter and vaporises almost entirely when wrecked. 125 and 126 spawn the destroyed versions. Intended for Mission 5, I assume? They have functioning hitboxes and can be destroyed, but no collision detection for the player; you can walk through them in either state. Cheers to Ernest Aguirre for the find.

ID: 127

A discoloured chunk of stone floor. It has no collision detection and is simply a foreground object. Seems it'd fit in with Mission 3. Cheers to Ernestro Aguirre for the find.

ID: 129

A small stone face; it has no collision detection, and is simply a foreground object. Seems ideal for the secret areas in Mission 3. A shrunk-down version of this sprite is depicted on the Pandora card. Cheers to Ernestro Aguirre for the find.

ID: 130

A chunk of stone or stalagmite. It has no collision detection, and is simply a foreground object. Cheers to Ernestro Aguirre for the find.

ID: 134

A piece of floor and ceiling from Mission 3. It has no collision detection, and is simply a foreground object... strange for what you'd expect to be background tiles, though. Cheers to Ernestro Aguirre for the find.

ID: 154 ~ 161

Destructible target practise posts; 154 and 158 will fall apart when shot twice, while the other IDs spawn the damaged pieces. Not sure where it'd fit outside of cutscenes or a "how to play" demo.

ID: 177 ~ 180

A hatch, with two variants for shutting and staying closed, and the floor beneath it as a separate object. It's appeared in games since Metal Slug 3, but is a no-show here and cannot be interacted with.

ID: 183

An underwater boulder, appears in the unused Slug Mariner stages. It can be destroyed but has no corresponding animation, it simply vanishes with no sound or debris.

ID: 196

A PF cadet in shackles? Harsh! Can be freed like any other POW. With the shadow baked into its animation, it can only be used in indoor locations, likely Mission 5 or the Dungeon.

ID: 200

A security camera that debuted in Metal Slug 3; this graphic appears baked into the background of Mission 5, but this is a separate sprite of its own. It swivels back and forth with an orange square beneath it, which disappears and reppears after every second rotation. Can't interact with the player, and you can't interact with it; there's no code to damage it from the looks of things.

ID: 202

A trio of cannons mounted on log platforms, almost surely meant for Mission 2; their positions line up smoothly next to the cave entrance on the second screen. They take turns firing homing missiles, and can be destroyed independently, though only one soldier will be shown ejected from the wreckage. The cannons' wreckage remains on-screen after they're both destroyed, though the "enemy destruction" debug dipswitch will completely erase it, which seems otherwise impossible in-game. Cheers to Ernesto Aguirre for the find.

ID: 204

The squid from Metal Slug 5, appears in the unused Slug Mariner stages. Is completely harmless until shot, at which point it turns red and charges forward, dealing damage.

ID: 205

A sea mine, also lifted from Metal Slug 5 and appears in unused areas. Inches towards the player on proximity.

ID: 208

A red zero? Can't be interacted with, and looks nothing like the usual HUD elements. Beats me, chief!

item ID: 0A, 0B, 0C, 0D, 0E

Big variants of the Heavy Machine Gun, Shotgun, Rocket Launcher, Flame Shot and Laser, with unused animated graphics! Picking them up plays no sound effect, and doesn't even give you the weapon. What a swiz.

item ID: 17

An item that randomly cycles through all the weapons, changing every second. Picking up the item displayed will give you that weapon. An unused item that's existed since Metal Slug 3, but has yet to appear in-game.

The IDs below are listed in decimal.

1 slug gunner??
2 black hound?
3 metal slug
4 slug gunner
5 black hound?
6 slug flyer
7 slug mariner (unused)
8 frogman
9 soldier in rubber ring
10 soldier in rubber ring
11 soldier - runs away
12 soldier - grenade
13 soldier - landmines
14 soldier
15 soldier - jumping knife
16 soldier - bottle rocket
17 soldier - rolling bomb
18 soldier - bottle rocket
19 soldier - grenade
20 soldier - crouching
21 ?
22 soldier - mortar
23 soldier - rifle
24 soldier - rifle, charging
25 soldier - rifle
26 soldier - bazooka
27 soldier - bazooka
28 soldier - bazooka
29 soldier - bazooka, emerging from hole
30 soldier - bazooka, emerging from hole
31 soldier - bazooka
32 soldier - bazooka
33 soldier - bazooka
34 soldier - bazooka
35 soldier - bazooka
36 soldier - bazooka
37 soldier - bazooka
38 soldier - bazooka, lying down
39 soldier - bazooka, hopping
40 soldier - bazooka, parachute
41 soldier - bazooka, parachute
42 ?
43 ?
44 ?
45 soldier - shield
46 soldier - shield
47 soldier - shield
48 soldier - shield
49 soldier - shield
50 ?
51 bat, aims for player
52 bat, swoops in arc
53 bat, static & indestructible?
54 japanese soldier
55 japanese soldier
56 japanese soldier
57 japanese soldier
58 japanese soldier
59 plane
60 ?
61 biker, slows to stop
62 biker, suicide crash
63 biker, suicide crash
64 ?
65 ?
66 ?
67 girida-o
68 girida-o
69 girida-o
70 girida-o
71 girida-o, looking up
72 girida-o
73 girida-o
74 girida-o
75 girida-o
77 r-shobu long heli
78 sarubia
79 melty honey
80 melty honey
81 melty honey
82 melty honey w/o shield
83 melty honey w/o shield
84 melty honey w/o shield
85 masknell
86 masknell
87 masknell discoloured?
88 masknell plummeting
89 r-shobu - bombs
90 r-shobu - missiles??? UNUSED????
91 r-shobu - missiles? acts a bit funky
92 pow - tied up
93 pow - tied to rope
94 pow - tied to pole
95 pow - freed
96 rumi aikawa - running away
97 rumi aikawa - running away
98 ?
99 ?
100 ?
101 ?
102 ?
103 ?
104 ?
105 box
106 treasure chest
107 ?
108 ?
109 ?
110 ?
111 ?
112 ?
113 ?
114 native - axe
115 native - scared, unarmed
116 missile launcher (launches too many!!!)
117 Allen Jr.
118 mission 1 boss
119 mission 2 boss
120 mission 3 boss
121 mission 4 boss
122 mission 5 boss w/ platforms
123 BIG GATE? UNUSED??????????
124 BIG GATE? UNUSED??????????
127 mission 3 floor
128 mission 3 floating platform
129 mission 3 face block?
130 mission 3 cave stone
131 "GO!" sign
132 "GO!" sign
133 mission 3 cave wall
134 mission 3 cave floor
135 mission 3 floating platform (can't interact)
136 mission 4 elevator
137 elevator?
138 mission 5 bookcase wall
139 mission 3 floating platform (can't interact)
140 mission 3 floating platform (can't interact)
141 mission 3 floating platform (can't interact)
142 mission 3 floating platform (can't interact)
143 mission 3 floating platform (can't interact)
144 mission 3 floating platform (can't interact)
145 mission 3 floating platform (can't interact)
146 mission 3 floating platform (can't interact)
147 mission 3 floating platform (can't interact)
148 mission 3 floating platform (can't interact)
149 mission 3 floating platform (can't interact)
150 mission 3 floating platform (can't interact)
151 mission 3 floating platform (can't interact)
152 mission 3 floating platform (can't interact)
153 mission 3 floating platform (can't interact)
155 UNUSED TARGET PRACTISE SIGN??? damaged, can't interact
156 same
157 same
158 same
162 mission 3 floating platform (can't interact)
169 ?
174 mission 5 platform (can't interact)
175 mission 5 platform edge (can't interact)
176 mission 5 wall
177 UNUSED HATCH - open
178 UNUSED HATCH - shutting
179 UNUSED HATCH - closed

180 dungeon floor
181 "GO!" sign
182 ?
184 dungeon "exit" sign
185 bullet
186 explosion
187 bullet
188 Walter
189 Tyra
190 logo (Japanese)
191 PF cadet - tied up
192 PF cadet - tied to rope
193 PF cadet - tied to pole
194 PF cadet - freed
195 PF cadet - in cage (you can interact with it!)
196 PF cadet - IN SHACKLES??? UNUSED???
197 "complete" level select icon
198 maggot
199 maggot cluster
200 security camera?? unused???
201 enemy submarine (mission 2)
202 enemy cannon platform UNUSED
203 wall cannon (mission 2)
204 squid UNUSED
205 sea mine UNUSED
206 ?
207 ?
208 red 0??? unused???
209 ?
210 bat