Sonic the Hedgehog 2 (Genesis)

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Sonic the Hedgehog 2

Developer: Sega Technical Institute
Publishers: Sega (JP/US/EU/AU), Tec Toy (BR)
Platform: Genesis
Released in JP: November 21, 1992
Released in US: November 24, 1992
Released in EU: November 24, 1992
Released in AU: December 1, 1992
Released in KR: November 21, 1992
Released in BR: 1992

This game has unused areas.
This game has unused code.
This game has unused objects.
This game has unused graphics.
This game has unused music.
This game has unused sounds.
This game has debugging material.
This game has a hidden level select.
This game has revisional differences.

This game has a development article

This game has a prototype article

This game has a prerelease article

This game has a notes page

This game has a bugs page

This game has a Data Crystal page

Sonic the Hedgehog 2 is the sequel to the first game, which introduces a playable Miles "Tails" Prower (unlike Sonic the Hedgehog 2 8-bit), the iconic Spin Dash, the idea of robot versions of Sonic, and an actual reward for collecting all ~~six~~ seven Chaos Emeralds, the golden-quilled Super Sonic. A large number of interesting things were cut from the final version, such as the mysterious and ever-famous level, the Hidden Palace Zone.

Sub-Pages

Development Info

Prototype Info

Prerelease Info

Notes

Bugs

Oddities
What do you mean, "the Special Stages have Perfect Bonuses"?

Revision Differences

Debug Functions

Level Select

Like the first game, Sonic 2 has a well-known level select:

Go into the Options menu.
In the sound test, play sounds 19, 65, 09, 17 (September 17, 1965 being Yuji Naka's birthday). This enables the Level Select.
Press Start to return to the title screen. When the menu appears, hold A and press Start to bring up the Level Select screen.

Debug Mode

Enabling the game's debug mode requires the level select to be enabled.

In the level select's sound test, play sounds 01, 09, 09, 02, 01, 01, 02, 04 (November 24, 1992 being the date of the game's US release).
Choose any level, then hold A and press Start. Keep A held down until after the title card pops up.

Alternatively, it can be accessed with Pro Action Replay code FFFFFA:0001.

From here, you have access to a variety of things:

Invincibility
Unlimited time
Debug coordinates (in place of score)
Sprite counter (in place of time)
Placement mode: Press B to enter placement mode. From there:
- Press A to move forward one object.
- Hold A and press C to move backward one object.
- Press C to place the object.
While the game is paused, some debugging options are available:
- Press A to go back to the title screen.
- Press and hold B to slow down the game by 50%.
- Press C to advance the game by one frame.

In addition, if Sonic dies, he can be revived by entering placement mode, moving to a safe spot, and exiting. Trying to place an object in this death state will freeze the game, however. You must also be playing as Sonic, as Tails cannot enter object placement mode.

"Night Vision" Mode

Go to the Level Select screen, enable Debug Mode, then hold C and press Start when selecting a level. This will cause the console's VDP to activate a debug function: background graphics drawn behind the sprite layer will be covered with a translucent black overlay.

Moving Background Debug

Use PAR code 00EBEC:4E71 (Rev. 00), 00EBC0:4E71 (Rev. 01), or 00EBC2:4E71 (Rev. 02) to enable a special debugging feature: Hold 2P Up or 2P Down to move the rising floor / lava in Hill Top and the moving clouds in the background of Wing Fortress.

(Source: Sonic 2 Disassembly)

Cheats

All 7 Emeralds: To get all 7 Chaos Emeralds, unlock the Level Select screen and play sounds 04, 01, 02, 06 or enter the Pro Action Replay code FFFFB1:0007.
Extra Continues: For 14 extra continues, play sounds 01, 01, 02, 04 on the Options screen. This cheat makes Oil Ocean Zone music play all the time due to an incorrect sound command.

Unused Graphics

Palettes

Graphic	Description
	Palette ID $03 (on the left) is the palette that was used for the level select until Beta 6; it remains in the final game and even in Sonic the Hedgehog 3, where it's still unused. Due to palette re-arrangement that happened during the title screen's overhaul, Sonic appears completely black while the background uses palette line 3, which is meant for Sonic. The palette cycle from Sonic 1's title, as well as the Sonic 1 Sega screen can be found at 0x1E5A, 0x26D6 and 0x26E2; the code for the Sega screen palette can also be found just above, entirely unreferenced.

Sonic

Graphic	Frame ID	Description
	52-53	An animation very similar to one used in Wing Fortress Zone when Sonic grabs the panels on the side of the ship. However, this is vertical. Sprites showing Knuckles in an identical pose also go unused in Sonic & Knuckles.
	5E	An alternate death frame, defined in animation 16. This returns from (and is also unused in) Sonic 1.
	CF	This sprite, though used, is incredibly obscure. It appears for only a single frame when turning from the "panic" balance animation, making it almost impossible to see under normal circumstances. It notably goes completely ignored in the mobile remake and Sonic Origins.

Dr. Eggman

Graphic	Name	Description
	Unused CPZ Animation	There's an unused animation for Eggman's Egg Poison mech accidentally dropping the Mega Mack on his own head in the Chemical Plant Zone fight. This animation has been around since the Nick Arcade prototype, but it was never implemented. The boss is programmed to play this animation whenever byte 0x2D (Obj5D_status) of its object RAM has its second lowest bit set, although it appears misaligned in the actual game. There's a fix to implement the lost animation here.
	Eggman laugh	In Death Egg Zone, Eggman is programmed to laugh when Sonic takes damage during the Mecha Sonic battle. However, as there are no Rings in this Zone, Sonic instead dies immediately when hit and all animation is frozen, so this is never normally seen without debug mode. In the 2013 mobile remake, this animation is not frozen when the player dies. You can also view the animation in the Sonic Jam port by playing in Easy mode, as well as the 3DS and Sega Ages versions by playing in Ring Keeper mode.

Other

Graphic	Name	Description
	Debug Font	All of the previous game's level select font still remains in the game. Only the numbers and letters A - F are used within debug mode. A majority of this is used in the prototypes for its own level select and error handler.
	HPZ Icon	A Level Select icon for Hidden Palace Zone. It is not normally used in any version of the game, but Pro Action Replay code 0096D8:0303 will cause it to replace the Emerald Hill icon in the Stage Select. It also appears in Sonic the Hedgehog 3's stage select, which contains icons for the Sonic 2 Zones. The final game's stage select wasn't implemented until Beta 7, while Hidden Palace itself was removed around the time of the Pre-Beta. Why this is here after the level was given up on, is anyone's guess.
	CPZ Decorative object	Unused decorative objects for Chemical Plant Zone, stored at 0x0383-0x0393 in VRAM. These can be placed in the iOS/Android 2013 version's debug mode.
	OOZ spring holder	A holder for the OOZ ball launcher (see below). This appeared in the Simon Wai prototype, and is still loaded into VRAM in the final game.
	Unused Aquis graphics	An unused animation for Aquis spitting up oil, along with an oil spray.
	Unused Balkiry frame	An unused frame of the Balkiry badnik from Sky Chase Zone with its landing gear deployed. It's possible that they were originally intended to take off from the Wing Fortress as it passed by. If a Balkiry is selected in debug mode, this sprite will be seen instead of its flying one.
	Walking Tocky	A walking animation for the Tockys in Sky Chase Zone. The only ways to see this sprite is by using debug mode to create and destroy a badnik while the Wing Fortress passes by, or by waiting to destroy a badnik when it passes by. This would later on make an appearance in Sonic Mania, shortly before the Metal Sonic boss battle at Stardust Speedway Zone.
	Picky	Picky, a returning animal from Sonic 1, is present in Death Egg Zone. However, there are no badniks or animal capsules, so he's never seen.

(Source: Sonic Retro)

Unused Objects

Object ID	Graphic	Name	Description
0C		CPZ Hovering Platform	This object has been around since the Nick Arcade prototype. Every 1024 frames, it will slowly rise up for 128 frames, float in the air, then come back down 128 frames later. The amount of time it floats in the air is 128*(lower four bits of subtype) frames. The upper four bits can be used to offset when it starts to rise in the air.
12		HPZ Blocker	This crystal was used in the earliest two prototypes to block off a tube in Hidden Palace Zone. The graphics are long gone, but the code is still there, such as it is. It's a simple solid indestructible object and its coding hasn't changed since the Nick Arcade prototype. In the 2013 remaster, it appears in the revised Hidden Palace as a breakable object, which often concealed springs, whereas the one that appears in the Proto Palace Zone warps the player back to the stage select.
13		HPZ Waterfall	Another Hidden Palace Zone leftover. Again, the graphics no longer exist in the ROM. Its height is equal to 16*(lower five bits of subtype)+16 pixels. Placing one with a subtype greater than 17 will spawn garbage objects on the right.
17	N/A	Green Hill Zone Spinning Spikes	A leftover from Sonic 1. Unfortunately, the graphics have been deleted, but the coding is intact.
46		OOZ Ball Launcher	A ball and spring object, which can be placed in Oil Ocean Zone via debug mode. If a switch is placed near it and pressed, the ball will pop out and start rolling in whichever direction Sonic was facing when the object was placed. It seems this object would have been used to cross something, as it can be stood upon, much like the boulder object that appeared in early versions of Sonic the Hedgehog. It does not collide with breakable floors or elevators, and it will go up slopes and even vertical walls without slowing or stopping. It can be seen in the Simon Wai prototype.
73		MCZ Ring Platform	An odd platform made of rings, which can be placed in Mystic Cave Zone via debug mode. It can be stood on, and moves in a similar motion to the spinning spiked balls in the level.
B7		WFZ Turbine Fire	If the sub-ID of the rotating platforms in Wing Fortress Zone has bit 02 of their subtype set but not 04, some kind of laser will appear (with no sound effects) when the platform spins. This object can be placed with debug mode, where it oddly appears before the used platform in the object list. As can be seen in this mockup screenshot, the colour and shape of the "laser" matches the thrusters on the underside of the Zone, meaning that this may have been its intended use. There isn't really any opportunity for this setup to be used anywhere in WFZ, as the thrusters are only found on the bottom of the ship, meaning there are no walls below them, and the spinning platforms are only ever found attached to walls.
BF		WFZ Destructible Pole	An odd spinning pole, which can be placed in Wing Fortress Zone via debug mode. It acts much like a Badnik: you can destroy it, and it can damage you, but it doesn't move. However, its sprites aren't grouped with the other WFZ Badnik graphics. Instead, they're placed alongside the other Wing Fortress level objects - specifically, right before the sprites for the spinning propeller blades. Based on this, it's possible the pole was meant for a destructible spinning propellers obstacle, as can be seen above. There are even markings on the sprite where the blades' ends can fit. (Source: "Wing Fortress's Unused "Badnik" Finally Solved?" on Sonic Retro)

Unused Subtypes

Graphic	Name	Description
	Monitors	If the subtype of a monitor is set to 00, the monitor will spawn with a static icon. Breaking the monitor will harm the player.
N/A	CPZ Tipping Platform	The amount of time that the platforms in CPZ can stay flipped is variable -- equal to 10+(upper four bits of the subtype) frames -- but in the final game, the upper four bits are always set to 70.
	ARZ Door	An unused door from Aquatic Ruin Zone, which like similar doors in other Zones closes as soon as the player enters it; this door was implemented between the Simon Wai and August 21st prototypes, but doesn't really seem to fit anywhere. These can be placed via debug mode.
	CPZ Bubble Snakes	The blue bubble snakes in Chemical Plant Zone have many subtypes that define their movement pattern (00-0F for jumping back and forth, 10-1F for jumping between the floor and ceiling) and their length, which can be any number of segments between 1 and 16. However, only those that are 6 segments long are used (subtypes 05 and 15), leaving all other subtypes unused. In addition, above the code to initialize the object is a table for varying vertical speeds, however it goes unused with the game instead using -$480; the unused values are -$500, -$600, and -$700. Attempting to use them in-game causes it to go beyond its limit, likely explaining why it went unused.
	OOZ Pressure Stopper	The used pressure stopper in Oil Ocean Zone launches the player upwards. If the object subtype is set to zero, as it is in edit mode, it will launch the player to the right. This would have been used in the Simon Wai layout of the stage, but has no purpose in the final layout.

Unlisted Objects

The code for the giant rings and the flash that goes with them from Sonic 1 is present in the ROM, but is not referenced by the object table, or in fact at all. The code is almost entirely unchanged from Sonic 1, but one notable oddity is that the giant ring is still designed to load the flash object, and only the line that actually assigned an ID to the loaded object is removed. The graphics for both are long gone.
Additionally, while the objects themselves are gone, the code for Sonic and Tails to interact with the sloped platforms from Marble Zone is still present in the game, also never referenced. It was completely rewritten to work for two players, but has a mistake in the code that makes the slopes not function properly. It seems to have been untouched since sometime before the Nick Arcade Prototype.

Unused Score Tally

This configuration for the score tally, replacing "ACT #" with "ZONE", is meant to be used in levels with only one act, such as Sky Chase Zone, Wing Fortress Zone, and Death Egg Zone. However, none of those levels have a score tally, so this text never appears unless a capsule is placed via debug mode and destroyed. This was later used in Hidden Palace Zone in the 2013 remake.

Unused Audio

Music

The song at entry #10 in the Sound Test is unused in normal gameplay; however, it will play if the corrupted remains of Hidden Palace are accessed in the final build through the use of cheating devices or otherwise hacking the game. It does not exist in the Simon Wai prototype, where instead the functional version of Hidden Palace uses the music that was later used for the 2-player version of Mystic Cave.

(Source: Sonic Retro)

Disc 2, Track 37 of the Sonic the Hedgehog 1&2 Soundtrack contains Masato Nakamura's original demo version of this song, but it doesn't loop and then fade out like the Zone demo tracks; instead, towards the end of the track, the tune changes significantly and has a proper ending. This may suggest that the music was originally intended for some sort of cutscene, perhaps taking place in Hidden Palace. Interestingly, this track is referred to as "STH2 Unused Song ~ Masa's Demo version ~", without specifying its intended use, though all track titles can be taken to be indicative only of how each song was used in the final release version.

Although popular speculation is that this song was at one point intended to be used as the background theme for Hidden Palace, the 2013 remaster of Sonic the Hedgehog 2 instead uses the same music as the Simon Wai, August 21st, and September 14th prototypes, as the developers felt that it better suited the revised level. However, this track later found use in the aforementioned remaster's "Proto Palace Zone".

Sounds

A few unused leftovers from Sonic the Hedgehog and other unused sounds can be heard in the Sound Test.

Sound ID	Sound	Description
Sonic the Hedgehog Leftovers
$29		The sound used when hitting the R, UP, and DOWN blocks in the Special Stage.
$31		Electricity sound from Scrap Brain Zone.
$38		Sounds similar to the sound of spikes popping up. This is also unused in Sonic 1.
$3A		The sound made while hitting the colored diamonds in the Special Stage.
$43		The warp noise made by a Giant Ring at the end of an act if Sonic enters it. This sound was later reused in Sonic the Hedgehog 3.
$47		Chain pulling sound from Marble Zone.
$49		Bonus point tag appearing at the end of an act.
Other Unused Sounds
$51		Unknown. Sounds like something popping or skidding on the ground.
$52		A low siren, similar to $53 which is used in the 2-Player mode.
$68		Appears to be a slightly shorter version of Mystic Cave Zone's bridges stopping in place ($69).

Scrapped Zone Remains

Zone ID 01

This is an empty level slot that exists in the game, which contained remnants of Labyrinth Zone in the Nick Arcade prototype. It can be accessed via Pro Action Replay code FFFE10:0100 or Game Genie code ACLA-ACD8 (AB6X-ACBR when locked-on to Sonic & Knuckles), and choosing "Sound Test" on the stage select menu (Special Stage with lock-on). This stage is an objectless version of Emerald Hill Act 1. Additionally, it has a Tails icon, much like the Wood Zone remains. Finishing Act 1 by hacking in an animal capsule will send you to Emerald Hill Zone Act 1. It reuses Emerald Hill Zone's animals, Ricky and Flicky.

Going by early concept art which shows roughly what the level order would have originally looked like, and lines up rather closely with the internal order, this slot was going to be used for a level called "Ocean Wind Zone".

Wood Zone (ID 02)

The original color palette is all that's left.

The level slot containing Wood Zone in the prototypes has something left in the final, albeit less than Hidden Palace: palette, palette cycle, start position, rasterized layer deformation data, background scrolling data, object data and music selection data. Accessing it via Pro Action Replay code FFFE10:0200 or Game Genie code ACLA-AECY (AB6X-AEBR with Sonic & Knuckles lock-on) and selecting Emerald Hill Act 1 (or by simply starting the game with the code active) or selecting Special Stage in Knuckles in Sonic the Hedgehog 2 in the level select leads to an objectless (since Wood Zone had no objects to begin with, even the debug object listing only has rings and teleport monitors) version of Emerald Hill Zone Act 1 with Wood Zone's palette, Metropolis Zone's music and some glitchy collision. Sonic uses Tails' life counter as the code points to it (in the Simon Wai and August 21st builds, this was Wood Zone's PLCs), and while locked on to Sonic & Knuckles the life counter's text is red. Playing this on Revision 02 and every version based on it (Mega Play Arcade, Knuckles in Sonic 2 and Sonic Classics) will have a scrolling glitch due to said versions removing its scrolling code. Some sprites from Metropolis Zone can be loaded into this zone. If you hack in an animal capsule and clear Act 2, you'll go to Metropolis Zone. It reuses Emerald Hill Zone's animals, Ricky and Flicky.

Zone ID 03

Another empty stage can be accessed with Pro Action Replay code FFFE10:0300 or Game Genie code ACLA-AGD8 (AB6X-AGBR with Sonic & Knuckles lock-on), and like with ID 01 above, it can be accessed by choosing "Sound Test" on the stage select screen (Special Stage with lock-on). This stage is nearly identical to ID 01, with the only differences being that some of the background is still intact, as well as the fact that it uses Oil Ocean Zone's theme as its default music. Badnik sprites from Metropolis Zone and Emerald Hill Zone are loaded. This level slot belonged to Emerald Hill Zone in the Nick Arcade prototype and then went unused in the Simon Wai prototype. Finishing Act 1 will send you to Emerald Hill Zone Act 1. It reuses Emerald Hill Zone's animals, Ricky and Flicky.

Going by early concept art which shows roughly what the level order would have originally looked like, and lines up rather closely with the internal order, this slot was going to be used for a level called "Sand Shower Zone".

Hidden Palace Zone (ID 08)

Various objects and items remain the same as they were in the Simon Wai prototype. This level was untouched since.

The level slot containing Hidden Palace Zone in the prototypes actually retains the level's object layout, palette, underwater palette, palette cycle, ring layout, but the art and block mappings point to Oil Ocean's 16×16 mappings, the level layout points to Oil Ocean Zone Act 1, the collision is from Oil Ocean's 16x16 Collision index, and the Badniks' code was removed. By using Pro Action Replay code FFFE10:0800 (30702E:0800 with Sonic & Knuckles lock-on) or Game Genie code ACLA-ATD4 (ACLA-ATDR in the "Rev. 00" version of the final, and AB6X-ATBR with Sonic & Knuckles lock-on) and selecting Death Egg in the level select (Special Stage in Knuckles in Sonic 2), you can see this for yourself. This level uses track 10 of the sound test (otherwise unused) and Oil Ocean's debug item list. The second Act can be accessed with the code AGLA-ATD4, and finishing it by placing an animal capsule with debug mode will take you to Oil Ocean Act 1. While locked onto Sonic & Knuckles, the game will automatically reset upon reaching the end of the stage.

Contrary to popular belief, this zone did have minor changes after the Simon Wai and August 21st prototypes. An object that forces Sonic into a ball was added inside the long tube near the start of the level and new background scrolling data. This was absent in all known prototypes. It otherwise seems to be identical to how it was in the Nick Arcade prototype, with the only difference being a lack of badniks, garbled graphics, and almost nowhere to stand on. Decorative objects, platforms, bridges, water, rings, shield, and Tails 1-Up monitors can be found if you use debug mode to navigate the level. Unlike the prototypes, striking this monitor does not grant an extra life, but it does while locked onto Sonic & Knuckles. It uses its own unique set of animals, Micky and Rocky.

Zone ID 09

Another empty level slot, which can be accessed by using Pro Action Replay code FFFE10:0900 or Game Genie code ACLA-AWD8 (AB6X-AWBR with Sonic & Knuckles lock-on) and choosing "Sound Test" (Special Stage with lock-on) in the level select. This version of the stage uses garbled Emerald Hill Zone tiles and badnik sprites from Oil Ocean Zone are loaded, has very little collision data, and no objects present within the debug menu, making it impossible to finish by any means. Just as it is originally the Simon Wai prototype, the default background music is the same as Sky Chase Zone. When finished by hacking in an animal capsule, you'll go to Emerald Hill Act 1. It reuses Hidden Palace Zone's set of animals, Micky and Rocky. This zone has water height listed however, this is likely just a leftover from HPZ.

Going by early concept art which shows roughly what the level order would have originally looked like, and lines up rather closely with the internal order, this slot was going to be used for a level called "Rock World Zone".

Zone ID 11

In Sonic 2's code, the pointers that controls the animals PLCs, list another entry after zone 0x10. This extra stage would've brought the total stage count up to 18, which was the amount that were originally planned. Attempting to load this stage will cause the game to crash on the title card as no other code references it, meaning necessary stuff like level art won't load and instead read garbage data. It reuses Sky Chase Zone's animals, Tocky and Cucky.

Unused Oil Ocean Zone Background Section

Oil Ocean Zone's background

Oil Ocean Zone's background layout is 768 pixels wide internally, but the game only uses the first 512 pixels. Sonic 2 has 64×32 tiles (512×256 pixels) loaded at a time, and loads new tiles on the edges as you move around the level. Oil Ocean's scrolling code doesn't reload any tiles as you move horizontally, leaving you with the same horizontal area of the background that you started with. This is because the standard tile-reloading mechanism would eventually overwrite the tiles used for the sun, which never moves. However, Chemical Plant Zone and Sonic 1's Scrap Brain Zone employ a more advanced method of reloading tiles that avoids this issue and would have been ideal for Oil Ocean, and yet Oil Ocean does not use it.

Unused Level Chunks

Emerald Hill Zone only:

01 - Used in the Nick Arcade and Simon Wai prototypes.
05 - Used in the Nick Arcade prototype.
0E - Used in the Nick Arcade and Simon Wai prototypes.
15 - Used in the Nick Arcade prototype.
17 - Used in the Nick Arcade prototype.
32 - Used in the Nick Arcade prototype.
56
7A
7F - Used in the Nick Arcade prototype.

Emerald Hill Zone or Hill Top Zone:

A6 - Used in the Nick Arcade and Simon Wai prototypes.
AE - Used in the Nick Arcade prototype.
D2
D8 - Used in the Nick Arcade and Simon Wai prototypes.
D9 - Used in the Nick Arcade prototype.
DA - Used in the Nick Arcade prototype.
DC - Used in the Nick Arcade prototype.
E7 - Used in the Nick Arcade and Simon Wai prototypes.
ED - Used in the Nick Arcade prototype.

Hill Top Zone only:

F5 - Used in the Simon Wai Prototype.

Chemical Plant Zone:

1D - Used in the Nick Arcade prototype.
4A - Used in the Nick Arcade prototype.
89 - Used in the Nick Arcade Proto, but it's completely different.

Casino Night Zone:

22
30
44 - Used in the Simon Wai Prototype.
48 - Used in the Simon Wai Prototype.
49 - Used in the Simon Wai Prototype.
50 - Used in the Simon Wai Prototype.
53 - Used in the Simon Wai Prototype.
54 - Used in the Simon Wai Prototype.
57 - Used in the Simon Wai Prototype.
5A - Used in the Simon Wai Prototype.
6D
6F
70 - Used in the Simon Wai Prototype.
72
77 - Used in the Simon Wai Prototype.
7C - Used in the Simon Wai Prototype.
EA

Mystic Cave Zone:

1E - Used in the Simon Wai Prototype.
3A - Used in the Simon Wai Prototype.
4F - Used in the Simon Wai Prototype.
88 - Used in the Simon Wai Prototype.
CA - Used in the Simon Wai Prototype.
CD - Used in the Simon Wai Prototype.
CE - Used in the Simon Wai Prototype.
CF - Used in the Simon Wai Prototype.
D0 - Used in the Simon Wai Prototype.
D1 - Used in the Simon Wai Prototype.
D7 - Used in the Simon Wai Prototype.
E6 - Used in the Simon Wai Prototype.

Oil Ocean Zone:

09 - Used in the Simon Wai Prototype.
2B - Used in the Simon Wai Prototype.
2C - Used in the Simon Wai Prototype.
59 - Used in the Simon Wai Prototype.
5E - Used in the Simon Wai Prototype.
62 - Used in the Simon Wai Prototype.
6D - Used in the Simon Wai Prototype.
73 - Used in the Simon Wai Prototype.
76 - Used in the Simon Wai Prototype.
79 - Used in the Simon Wai Prototype.
81 - Used in the Simon Wai Prototype.
84 - Used in the Simon Wai Prototype.
86
8A - Used in the Simon Wai Prototype.
94 - Used in the Simon Wai Prototype.
97 - Used in the Simon Wai Proto, but it's completely different.
9E - Used in the Simon Wai Proto, but it's completely different.
A0 - Used in the Simon Wai Prototype.
A5 - Used in the Simon Wai Prototype.
A6 - Used in the Simon Wai Prototype.
A9
AA - Used in the Simon Wai Prototype.
B2 - Used in the Simon Wai Prototype.
BC - Used in the Simon Wai Prototype.
CC - Used in the Simon Wai Prototype.
D0 - Used in the Simon Wai Prototype.
D2 - Used in the Simon Wai Prototype.
D3 - Used in the Simon Wai Prototype.
D6 - Used in the Simon Wai Prototype.
DB - Used in the Simon Wai Prototype.
DC - Used in the Simon Wai Prototype.
DE - Used in the Simon Wai Prototype.
E0 - Used in the Simon Wai Prototype.
E9 - Used in the Simon Wai Prototype.
EA - Used in the Simon Wai Proto, but it's completely different.
F0 - Used in the Simon Wai Prototype.
F5 - Used in the Simon Wai Prototype.
F6 - Used in the Simon Wai Prototype.
F8 - Used in the Simon Wai Prototype.
F9 - Used in the Simon Wai Prototype.
FF - Used in the Simon Wai Prototype.

Note that none of the unused chunks are in the table that the game checks to determine whether or not Sonic & Tails should slide.

Metropolis Zone:

03 - Used in the Simon Wai Prototype.
69 - Used in the Simon Wai Prototype.
79
7D - Used in the Simon Wai Prototype.
8A - Used in the Simon Wai Prototype.
B6 - Used in the Simon Wai Prototype.
D0 - Used in the Simon Wai Proto, but it's completely different.
D5 - Used in the Simon Wai Proto, but it's completely different.
DC - Used in the Simon Wai Prototype.

Wing Fortress Zone:

43
48
4F
57
62
98
DD

Unused 2x2 Tiles

Tiles loaded in the VRAM are organized by tileset at RAM address FF9000. IDs are created at this point for each line, representing 2x2 chunks of VRAM graphics. Address FF0000 is in charge of adding mirroring and collision to the 2x2 tiles, creating 8x8 chunks. In all, there are 256 chunks created from FF00000. To add these chunks, add the IDs below in the format 0xxx at FF0000, and search for chunk ID 00 in the stage data. Some unused graphics can be found in this way:

Zone	Plane A Low	Plane B High	IDs
Oil Ocean Zone			017, 01B, 081, 08D, 093, 0B2, 0B3, 0C8 0C9, 0D0, 0D1, 0DB, 0DC, 0F3, 0F4, 114 11C, 11D, 11E, 123, 124, 125, 126, 127 128, 129, 12A, 12B, 12C, 12D, 12E, 12F 130, 131, 134, 139, 13A, 13F, 141, 144 146, 147, 157, 15B, 182, 183, 184, 187 189, 18A, 18E, 1AB, 20F, 210, 216, 217 218, 250, 25E, 262, 263, 270, 272, 27E 28A, 28B, 293 This mapping includes several unused graphics, one of the better-known ones being used in the Simon Wai prototype for the spring-and-ball object.
Metropolis Zone			023, 024, 025, 026, 028, 029, 048, 049 04A, 04B, 04C, 04D, 04E, 04F, 050, 051 052, 053, 054, 055, 056, 057, 058, 059 05A, 05B, 05C, 05D, 05E, 05F, 060, 061 062, 064, 065, 066, 067, 068, 09F, 0C2 134, 135, 136, 137, 138, 139, 13A, 13B 13C, 13D, 13E, 13F, 140, 141, 142, 143 144, 145, 147, 174, 17B, 196, 197, 198 199, 19A, 19B, 19C, 19D, 19E, 1A1, 1A2 1AF, 1B0, 1B1, 1B2, 1B3, 1B4, 1B5, 1B6 1B7, 1B8, 1B9, 1BA, 1BB, 1BC, 1BD, 1BE 1BF, 1C0, 1C1, 1C2, 1C3, 1C4, 1C5, 1E4 1E6, 1E7, 1E8 Some leftovers from the level design of the trapezoid lift area from the Simon Wai prototype, as well as some unused silver pipes that were possibly intended for background decoration.
Sky Chase / Wing Fortress Zone			147, 14D, 151, 157, 162, 16C, 1BB, 1F8 1FE, 1FF, 201, 210, 211, 215, 219, 21A 227, 228, 259, 262, 268, 27C, 2A0, 2A2 2B7, 2E3. Not too much interesting, except for some kind of railing and various tiles with unused graphics and clouds for use in Sky Chase.

Unused Scrolling Code

Aquatic Ruin Zone

The routine that controls Aquatic Ruin Zone's scrolling sets up three layers of parallax for the rows of leaves found floating high above the level. The code sets up these layers to scroll at different speeds, but the speeds of the top and bottom layers are immediately overwritten with the speed of the middle layer afterward, effectively disabling the parallax. This behavior goes all the way back to the Simon Wai prototype version of the level. If re-enabled, the parallax effect will split some of the leaves in half due to how the layers are separated, suggesting that the effect was designed for an earlier version of the level art, or that it was simply cut for looking rough.

(Source: Clownacy)

Hill Top Zone

Basic scrolling code exists for a two-player version of Hill Top Zone. This code appears to be unfinished, as it lacks the parallax movement of the cloud layer present in the one-player version of the level. This alone should not be taken as evidence of a two-player version of the level being planned, however, as Hill Top's moving objects lack the flag that stops them from despawning whenever the player moves out of their range. This flag is used by moving objects found in all other two-player levels and is required for compatibility with the two-player mode's special object management system. In addition, the level's earthquake gimmick and the faraway scrolling mountains in the background, as well as various enemy graphics, are completely unoptimized for two-player mode.