Sonic the Hedgehog 3

Sonic the Hedgehog 3
Also known as: Baramdori Sonic 3 (KR) Developer: Sega Technical Institute Publishers: Sega (JP/US/EU), Samsung (KR), Tec Toy (BR) Platform: Genesis Released in JP: May 27, 1994 Released in US: February 2, 1994 Released in EU: February 24, 1994 Released in AU: March 1994 Released in KR: 1994 Released in BR: March 1994 This game has unused animations. This game has unused areas. This game has unused playable characters. This game has unused code. This game has unused enemies. This game has unused objects. This game has unused graphics. This game has unused items. This game has unused abilities. This game has unused music. This game has unused sounds. This game has debugging material. This game has a hidden sound test. This game has a hidden level select. This game has regional differences. This game has revisional differences. This game has a prototype article This game has a prerelease article This game has a bugs page This game has a Data Crystal page

Sonic the Hedgehog 3 is the third game in the 16-bit Sonic trilogy and the first game with the easily-tricked-by-Eggman redheaded echidna, Knuckles. Originally one big game, Sonic 3 was split into two games due to time constraints, cartridge costs, and a promotional deal with McDonald's; the second half of the story is its direct sequel, Sonic & Knuckles.

To do: There's still a lot more to be documented from the S3 Unlocked blog. Leftover object mappings still exist for dummied out objects. Apparently, unused bytes of sequence data exists in some of the music for the game. Investigate it and add it to the article. Launch Base Zone Act 2 has words writted in tiles briefly before the Death Egg graphics load. Can these be isolated?

Sub-Pages

Prototype Info

Prerelease Info

Bugs

Sonic & Knuckles Leftovers All sorts of leftovers from the game still in development.

Unused Graphics Atta, Tails!

Level Select/Debug Mode

To access a level select and debug mode, press Up, Up, Down, Down, Up, Up, Up, Up after the SEGA logo screen fades to black and Sonic begins to move, but before the title screen appears (about 4.31 seconds after boot). You only have about 1.3 seconds to enter it, and due to this screen having an absolutely ridiculous number of lag frames, it may not always work; you'll hear the ring collection sound if you did it right. Then, to find the level select on the title screen, simply press Up to reveal "SOUND TEST" and press Start. In the Sonic Jam version of the game the code is entered on the title screen and no precise timing is required. Alternatively, you can unlock the level select by these alternate methods:

• You can access the leftover Sonic 2 Options menu (see below) and enter the Sonic 2 level select code in the sound test (19, 65, 09, 17).
• You can also use Game Genie code AA6T-AAXC or Pro Action Replay code FFFFD0:0100 to access the level select.
• If you are playing on a real Mega Drive/Genesis console and don't mind risking the long-term health of your console and cartridges, then another method is to load up Sonic 2, unlock its level select (19, 65, 09, 17 in the sound test), swap the cartridge with Sonic 3 without turning the power off, and then press Reset. This works because the RAM variable that unlocks the level select is preserved when you reset the console (Sonic 3 was built upon the Sonic 2 source code, and thus shares a number of RAM variables).

Pressing C on the level select screen increments a counter that determines the players' characters in the Competition mode Zones, with the first controller incrementing the left counter and the second counter incrementing the right:

• 00 - Sonic
• 01 - Tails
• 02 - Knuckles

Play sounds 02, 04, 05, 06 in the sound test to get All Emeralds. A Chaos Emerald sound will confirm correct entry.

Debug Mode

To activate debug mode, select a file/level, hold A and press Start, and keep holding A until the level begins. You can also hold C and press Start to highlight high-priority background tiles (tiles that overlap Sonic and other sprites). While in debug mode, you have access to the following:

• Infinite time
• Debug coordinates (in place of score)
• Sprite counter (in place of time)
• Placement mode: Press B to enter placement mode, which allows you to move Sonic anywhere in the level with the D-Pad and place objects from a predefined list (not all objects may be available in a given level). In this mode:
  • Press A to move forward one object.
  • Hold A and press C to move backward one object.
  • Press C to place the object.
  • Press B again to return to normal gameplay.
• Character animation viewer: hold C and press B to rapidly cycle through all available animation frames for the current character (pause the game and use frame advance to view individual frames). Press B again to return to normal gameplay.
• Pause options:
  • Press A to go back to the level select.
  • Hold B to progress the game in slow motion.
  • Press C to advance one frame.

If you die, press B to enter placement mode, and then press B at a safe spot to revive yourself. Do not enter debug mode at any point where Sonic's sprite rotates (such as while standing on the red-and-white cylinders in Carnival Night Zone) or the game will crash.

Secrets

The level select menu shows what the level order was at one point. The Sonic 3 Zones are in their normal order, but Flying Battery from Sonic & Knuckles is listed between Carnival Night and IceCap. Following Launch Base are Mushroom Valley (an early name for Mushroom Hill) and Sandopolis, but neither of those can be selected. The Sonic & Knuckles bonus stages are also listed in the level select but none of them can be selected.

According to commentary from the Sonic Jam strategy guide, IceCap was meant to follow Flying Battery as Sonic was supposed to break down the door at the end of the latter Zone and use it as a snowboard. There's also a variety of unused songs, all from Sonic & Knuckles, in the sound test.

Furthermore, all the graphics here (including the level icons) are recycled from Sonic the Hedgehog 2, and the icons are shown in the Sonic 2 order, such as Emerald Hill's icon for Angel Island and Casino Night's icon for Carnival Night. Interestingly, the second "2P VS" entry shows the unused Hidden Palace icon.

Sonic 2 Menu Leftovers

By setting the game's screen mode to $24, you can access the Sonic 2 options menu in Sonic 3! Alternatively, you can use the patch code FFF600:2400 or hack the menu back in yourself.

As all the options here can be selected normally through other means in Sonic 3, the only real benefit of this is entering the Sonic 2 level select code to access it in Sonic 3.

It's also possible to find the 2-player Level Select from Sonic 2 using the patch code FFF600:1C00. However, each Zone is X'ed out and it plays an error sound when you press Start, so you can't really do anything with this menu. Data for the Sonic 2 Results Menu also exists, but it can't be seen.

Leftover graphics from the Results Menu can be found.

Eighth Special Stage

Map	In-Game

There is an eighth Special Stage with a grey Chaos Emerald (much like the fifth Emerald) that is inaccessible during normal gameplay. To access it, open the level select, set the sound test selection to 07, then hold A and press Start on "Special Stage 2".

The stage is fully playable, although it may occasionally slow to a crawl when collecting a blue sphere, which may have contributed to its removal. The Emerald has no special effect in-game, and does not appear on the end-of-stage tally in any form other than a score increase. The complete lack of rings also makes it impossible to get a Perfect Bonus on this stage.

Sonic Mania would reuse this layout for a Bonus Stage, replacing some of the blue spheres with rings to allow a Perfect Bonus.

(Source: Sonic Retro)

Water Levels in Launch Base Zone Act 1

There are 5 areas containing water in Launch Base Zone Act 1 that either raise or lower the water level in some specific areas. From this, it's not unreasonable to assume both Acts of LBZ would contain water .

To view these levels, add the patch code FFF730:0100 and change VDP 0x04 to 0x14. The water levels can be seen in the ROM at address 0x5350.

The first level can be seen in the ROM address at 0x51EE and should increase the water level to 0A80, but doesn't due to an error.

The second level is located from 0000 to 0E00 and raises the water to 0B00.

The third level is located from 0E00 to 2340 and raises the water to 0A00

The fourth level is located from 2340 to 2C00 and lowers the water to 0AC8.

The fifth level is located from 0AC8 to FFFF and makes the water disappear.

Unused Objects

ID	Offset	Name	Image	Description
0B	0002336E	Red Revolving Spheres		A spinning mass of red spheres, which can be placed in the first half of Angel Island Act 1 via debug mode. The spheres resemble those that appear in the game's special stages, but the object itself seems to have no apparent gameplay purpose. When it is placed, many palette and VRAM complications occur in the level, and the game slows down considerably. The object can be manipulated with the second controller. Up - Rotates the object vertically. Right - Rotates the object horizontally. Down/Left - Moves the object up or down. A/C - Changes the object's size. B - Rotates the object sideways. Start - Toggles automatic rotation. A similar object appeared in a tech demo that served to test the 3D mechanics of the Special Stages, seen in the November 3rd, 1993 prototype. However, the objects are not identical, and the one used in the tech demo subsequently does not exist in the final version of Sonic 3.
N/A	000?????	Unused Foreground Tree Sprite		Despite its similar appearance to the trees seen at the end of Angel Island Zone Act 2 when Eggman flies through the forest, this is actually a separate object entirely that goes completely unused. It's meant to be placed in the foreground, and its graphics are located with the unused switch graphics, suggesting it may have been used earlier in development. It can be placed with debug mode.
0D	0001F6BC	Breakable Wall		A breakable wall, placeable in Angel Island Act 2 using debug mode. It comes in two variations: one that acts as a wall obstacle that can be destroyed with the Spin Dash, and one that acts as a door that opens with a switch.
33	0002BB20	Carnival Night Button		A button of unknown purpose. It can be placed in either Act of Carnival Night Zone via debug mode, but it doesn't appear to do anything. Also unused in Sonic 3 & Knuckles. Knuckles (Sonic/Tails' story) pushes a button like it in Act 2 to darken the place.
??	000?????	Carnival Night Ring Object		An unknown object that appears to spawn slope collision when placed. It was likely used for Testing slopes.
2A	0002963A	IceCap Breakable Block		A glowing block that can be placed in either Act of IceCap Zone via debug mode. Jumping on it destroys it like the ice blocks. Also unused in Sonic 3 & Knuckles. It has a subtype of 1A.
08	00022612	Competition Mode Spikes		A set of spikes for Competition Mode. Spikes do not appear in any of the five courses, but they can be placed with debug mode.
12	00024722	Unused Elevator		An unused elevator object defined as object ID 12. The graphics no longer exist, but the leftover symbol name of elev06 in Sonic & Knuckles Collection seems to indicate it was intended for Launch Base Zone, possibly before the new elevators were created. It can be operated using a switch.
1A	00026202	Rotating Platform		A kind of spinning platform-like object with undefined graphics, with object ID 1A. When touched, it locks the player to the center of the object; the faster the player runs, the further they're thrown after exiting it. However, this behavior is likely an unintended side effect of a bug in the object's code. If the bug is fixed, it behaves more logically like a standard rotational obstacle. The rotation of the object can be manipulated using the second controller. It was labeled as rollita in Sonic & Knuckles Collection's symbol data. This object may also have been created for Launch Base Zone.
1C	000268FE	Spinning Structure		A curious object that damages the player if hit from above, but swings from side to side if hit from below. Its graphics have not been found, and its animation resembles something turning. Identified as Object 1C. It may also have been created for Launch Base Zone.
1D	0002425E	Grabbable Platform		A normal platform with a grabbable bottom. The bottom portion of the graphics are corrupted, but it seems to fit Launch Base Zone the best. Its ID is 1D.
27	0001C704	Leftover Lava Damage Object		This object was used in Sonic 1 and Sonic 2 to damage the player when they touch lava, but doesn't work here. It's possible to change the size of the area by modifying its variable. ID 27.
3D	00022072	Up and Down Spring		Intended for Flying Battery Zone, this object creates a spring that goes up and down temporarily. It also bounces the player abnormally high. Identified as ID 3D.
N/A	000?????	Big Sonic on the Sega Screen	N/A	There is leftover code from the large Sonic on the Sega screen in Sonic 2. The object seems to be a fairly old leftover as it is still using the old Sonic 2 object format. The sprite mappings still exist.
N/A	000?????	Shield Object	N/A	Code for a fourth type of shield exists inside of the ROM. The shield itself is the ordinary non-elemental shield as seen in Sonic 1 and Sonic 2. It is unknown whether or not this is simply a leftover, or if it was originally planned for the game. It is worth noting that the shield sound from Sonic 2 remains unused in the sound test. Interestingly, it exists under three valid monitor shield subtypes: 00, 02 and 03. You can activate this shield type manually by changing RAM address FFB02B:00 to 01 or using Action Replay Code "FFB02B:0001".

Other Unused Objects

Many of these have their programming intact in the November 3, 1993 prototype, but not compiled (or loaded) in the final version's binary. (However, Gapsule still has its code due to Flying Battery's late removal from Sonic 3.)

Object ID	Name
84	Hey Ho, the boss of Mushroom Hill Zone Act 1.
8F	Gapsule, the boss of Flying Battery Zone Act 1.
90	Fireworm
91	Iwadomoki
92	Toxomister
93	Madmole
94	Mushmeanie
95	Dragonfly
96	Butterdroid
97	Cluckoid
98	Guardian, the Sandopolis Zone Act 1 boss.

Unused S&K Mapping Data

In Sonic 3 there remains some leftover sprite mapping data for Sonic & Knuckles objects, largely consisting of badniks that would have appeared in the Sonic & Knuckles zones.

Name	Sonic 3	Sonic & Knuckles	Description
Flying Battery Act 2 Mid-boss			The laser beams of the laser turret were extended, most likely to be able to penetrate the floor. Most likely also caused by the differences in the boss arenas of Flying Battery Zone between the prototype and Sonic & Knuckles.
Iwadomoki			The Sonic 3 mappings use palette line 4 for the rock body. Sonic & Knuckles changes that part to palette line 3, most likely to make it blend in with the stage.
Toxomister			The body and head of this badnik were swapped around.

Unused Audio

Music

Most of the music from Sonic & Knuckles can be played from the Level Select/Sound Test.

Sound ID	Audio	Name with Comments
$09		Flying Battery Zone Act 1. The loop point in the "echo" track of the lead instrument is set slightly later than the rest of the tracks; as a result, it falls further and further out of sync every time the song loops. This was fixed in Sonic & Knuckles and Sonic 3 & Knuckles. For some reason, this version of the song was used in Sonic Origins, but since the audio was converted to a streamed format, the desync isn't as noticeable.
$0A		Flying Battery Zone Act 2.
$0F		Mushroom Valley/Hill Zone Act 1.
$10		Mushroom Valley/Hill Zone Act 2.
$11		Sandopolis Zone Act 1.
$12		Sandopolis Zone Act 2.
$13		Lava Reef Zone Act 1.
$14		Lava Reef Zone Act 2/Hidden Palace Zone.
$15		Sky Sanctuary Zone.
$16		Death Egg Zone Act 1. For some odd reason, this plays in Sky Sanctuary Act 2 in Sonic 3 alone.
$17		Death Egg Zone Act 2. Death Egg Zone uses this for acts 1 & 2 in Sonic 3 alone.
$18		Sonic & Knuckles Act 1 Boss. This can be heard while fighting any Hydrocity Zone boss if you jump out of the water after the drowning music starts.
$1A		The Doomsday Zone.
$1B		Glowing Spheres Bonus Stage.
$1D		Slot Machine Bonus Stage. Oddly, the unused Glowing Spheres Bonus Stage in Sonic 3 alone uses this music.

(Source: Sonic Retro)

Sound Effects

Many of these sound effects would see use in Sonic & Knuckles, though some of these sounds would also be unused there.

Sound ID	Sound	Comments
$3A		This is a shield sound leftover from Sonic the Hedgehog 2.
$40		Unused; sounds like an electric zap. This sound would later be used for the Thunder Shield in Sonic Generations and Sonic Lost World, suggesting that it may have been an early sound effect for the Thunder Shield. The Phantom Egg also uses this sound for its barrier in Sonic Mania. The concept art found in Sonic Origins suggests that this would have been the sound for the Thunder Shield with the one used in-game used for the otherwise scrapped and repurposed "Magnet Shield", later as a simplistic power up in Sonic Superstars.
$53		Laser charging sound, used for the Flying Battery Zone laser boss and the jumping spike balls in Lava Reef Zone Act 2.
$54		Laser firing sound, used for the Flying Battery Zone laser boss.
$55		Sound effect used when a brick in Sandopolis Zone goes across a line of black rotating circles.
$5A		Unused; sounds like something revving up. This sound effect would see use in Sonic 3D Blast.
$5C		The sound of Mecha Sonic short-circuiting after it's defeated.
$69		The sound that plays when you push a brick in Sandopolis Zone.
$6B		Unknown, possibly unused; sounds like a higher-pitched version of the sound heard when hitting an R, Up or Down block in the Special Stage from Sonic 1.
$6D		Unused; sounds like a door closing.
$71		Duplicate of $3A; another shield sound leftover from Sonic the Hedgehog 2.
$7A		The sound of the Lava Reef Act 2 boss emerging from lava.
$7C		Used by the magnetized platforms in Flying Battery Zone.
$7D		Unused; sounds like mild rattling.
$84		Unused; sounds like something charging up. Only seems to be referenced in some zone with a high level ID which is composed of garbage data.
$85		Unused; sounds like it would have been used in cooperation with $84.
$87		The sound that plays when you bounce on a mushroom in Mushroom Hill Zone.
$88		Mushroom Hill Zone elevator sound.
$89		Mushroom Hill Zone satellite dish (from Dr. Eggman's season-changing machine).
$8A		The sound the ghosts from Sandopolis Zone make when they vanish.
$8B		The sound of the Mushroom Hill miniboss chopping a log.
$8C		The sound of the Mushroom Hill miniboss struggling to chop a log.
$8D		Unknown, possibly unused; a very quiet sound. Could have been used as waterfall ambience like in Sonic 1?
$8E		Unused; another electric rev-up sound. This sound is used in the Sonic Origins remake for the spinning wheels in Marble Garden.
$8F		The sound the door on the pyramid in Sandopolis Zone makes when it opens.
$90		Door closing sound from Sandopolis Zone, and also the sound of Knuckles hitting the ground after his defeat.
$92		Ghost sound effect from Sandopolis Zone.
$93		The sound that plays when the armor on Dr. Eggman's golem machine comes back on. This sound was reused later in Sonic Mania as the sound for the Green Hill Zone Act 1 boss spinning.
$95		The sound of the giant hand appearing to attempt to crush you in the Lava Reef miniboss.
$96		The sound the giant spikeballs in Lava Reef Zone make when they roll around.
$97		The sound a Toxomister makes when it sprays its toxic gases.
$98		The sound of a falling stalactite in Lava Reef Zone.
$99		Unused; A small "tick" sound.
$9A		The sound of the pop-up springs from Sky Sanctuary Zone.
$9B		A loud bang that plays when the Sandopolis Zone Act 2 boss comes closer to you.
$9C		Sound that plays when a Super Emerald regains its color.
$9D		The sound of the missile reticles in the Lava Reef Act 2 boss. This sound effect is also used by the Green Hill Zone Act 2 boss from Sonic Mania.
$9E		The sound of a platform breaking upon coming into contact with the Lava Reef Act 2 boss.
$A0		The sound of the Lava Reef Act 2 boss firing a missile.
$A1		Unused. A low-humming, unsettling sound. This sound effect is used by the Stardust Speedway Act 1 boss in Sonic Mania.
$A2		The sound of the speed-up launchers in Flying Battery Zone and Death Egg Zone.
$A3		Death Egg Zone lift platform sound effect.
$A4		The sound that Mecha Sonic makes when he goes super.
$A5		Unused; sounds like something rising or powering up?
$A6		Unused; another dashing noise.
$AE		The sound that the seesaw mushroom from Mushroom Hill Zone makes when the black weight lands on it. This sound is also used in the Bonus Stages in Sonic & Knuckles.
$B5		A leftover from Sonic 1 that was used for the breakable diamonds in the Special Stage. Might have been used for the Slot Machine Bonus Stage which is based off that Special Stage.
$BC		Unused? Possible waterfall sound effect.
$C2		The sound of the flamethrowers in Flying Battery Zone and Lava Reef Zone.
$C4		The sound Red Eye makes when it gets angry.
$C5		Unused; sounds like it would be used in coordination with $C4. Later used in Sonic Origins for when Red Eye calms down.
$CA		The sound of the light beam transportation systems in Death Egg Zone.
$CE		The gusts of wind from Mushroom Hill Zone. Also used in Knuckles' ending after Super Mecha Sonic explodes.
$CF		A louder version of $CE that might be unused even in Sonic 3 & Knuckles.
$D1		Possibly unused; another very faint sound that may sound like static.
$D3		Used in Sonic & Knuckles when the Death Egg flies through Sky Sanctuary zone; sounds like a quiet version of $CD.
$D4		Used by the bouncing puzzle room in Death Egg Zone.
$D5		Used when the lava falls from Lava Reef Zone. Repeatedly pressing the C button when playing this sound in the Sound Test makes it play longer.
$D6		Unknown/unused; rumbling/electric sound?
$D7		The sound of the elevators in Lava Reef Zone and Death Egg Zone.
$D8		Unused; sounds like a screeching warning siren. Repeatedly pressing the C button when playing this sound in the Sound Test makes it play longer.
$D9		The sound the electromagnets in Flying Battery Zone and the black gravity spheres in Death Egg Zone make.
$DA		The sound of the wind trap Knuckles activates in Mushroom Hill Zone.
$DC - $DF		All of these sounds are duplicates of $DB (heard when running across water in Hydrocity Zone) and are likely placeholders. Sonic & Knuckles replaces $DC with its credits medley.

DAC samples

To do: Replace disassembly names with accurate descriptions of what the samples are.

Plenty of DAC samples also go unused.

DAC ID	Sound	Comments
$89		Referenced in the disassembly as "dRideCymbal"
$96		Referenced in the disassembly as "dLooseSnare". This is used in the November 3rd prototype's credits music.
$9A		Referenced in the disassembly as "dMidTimpaniS3"
$A6		Referenced in the disassembly as "dDanceSnare"
$A7		Referenced in the disassembly as "dLooseKick"
		A completely unreferenced DAC sample, placed between samples $AF and $B1 in ROM.
$B8		Referenced in the disassembly as "dHipHopHitKick2"
$BD		Referenced in the disassembly as "dPowerKick2"

Unused Palettes

Offset	Name	Graphic	Comments
08C134	Sonic 2 SEGA Screen		The color palettes of the Sonic 2 SEGA screen.
08C1B4	Sonic 2 Title Screen		Tails' color palette from the Sonic 2 title screen.
08C1D4	Sonic 2 Prototype Level Select		The color palettes of the prototype Sonic 2 level select.
08CB14	Early Launch Base Zone Act 2 Water	November 3rd 1993 Palette Unused Palette	This palette set does not include colors for Sonic underwater, which suggests it would be used after some cutscene or scene change in Launch Base Zone. It closely matches up with the November 3rd prototype's Act 2 water palette.
08CDB4	Glowing Spheres Bonus Stage		Remains identical to the November 3rd prototype.
08CE14	Slot Machine Bonus Stage		Remains identical to the November 3rd prototype.
002EFE	Lava Reef Zone Cycle 1		The palette cycle for the lava in Lava Reef Zone. Can be seen if Lava Reef is accessed in Sonic 3.
002F7E	Lava Reef Zone Cycle 2		The palette cycle for the dark glowing rocks in Lava Reef Zone. Can be seen if Lava Reef is accessed in Sonic 3.
05275C and 05277C	Act 2 Enemy Palettes		Copies of the enemy palettes from Angel Island Zone Act 2 and IceCap Zone Act 2. They were once used by the post-boss cleanup routine to reset the palette during the Act 1 results, since the Act 2 palette for those stages is loaded before the Act 1 boss. In the final game, the same routine points at the actual Act 2 palettes instead, making these redundant.
08C2F6	Unused Knuckles 1-Player Palette		Knuckles' 1-player palette in Sonic & Knuckles. NPC Knuckles uses a modified palette to avoid clashing with the HUD; due to them sharing the same palette line, Knuckles' green socks would cause the HUD to turn green during cutscenes. Features redder fur colors compared to NPC Knuckles due to the palette having been modified since the November 3rd prototype; NPC Knuckles' palette wasn't adjusted to reflect it.

Scrolling Credits

The game contains an unused, unfinished scrolling credits routine, which can be activated by setting RAM address FA87 to 2 during the credits sequence or using Pro Action Replay code FFFA87:0002. The actual credits were apparently not yet in place when this was abandoned, as it scrolls small and large versions of the letters B-F, and then abruptly fades to the Sonic 3 logo screen. The final staff roll simply fades between static pages of text.

Unused Areas

Name	Graphic	Comments
Hydrocity Zone Act 1		The starting corridor from Act 2 is present in the Act 1 layout; even though it gets overwritten and ends up unused. The boss arena from this act is present in the Act 2 layout.
Carnival Night Zone Act 1		A long unused corridor in Act 1 that starts at coordinate 3400 to 3800 at the high 04AC is very similar to Act 2 when Act 1 is rewritten after the fight against the mini-boss. However, this corridor is at a height above the rewritten area and is never seen.
Carnival Night Zone Act 2		There is a long vertical shaft at the very end of the level. It leads down into a bottomless pit. The shaft serves no apparent purpose and is never seen normally.
		Knuckles' ending area and teleporter are all still intact. The teleporter is non-functional however.
IceCap Zone Act 1		Knuckles' starting location can still be found in IceCap Zone even though it goes unused.
Launch Base Zone Act 1		A small level section and spring are in the Launch Base Act 1 layout. Just like Hydrocity Zone, they are part of the Act 2 layout, but get overwritten by their act 2 counterparts.

Oddities

Misplaced Objects

Graphic	Comments
	There are 3 "end-of-act monitors" hidden in the boss area in the Carnival Night Zone Act 2 contain 10 rings each, curiously there are also monitors in the area of the boss on Angel Island 2 on the way to Knuckles. This is still a total mystery.
	A piece of bridge can be found inside the walls of Hydrocity Zone Act 2.
	An ice spike can be found inside the walls of the IceCap Zone Act 1, near the end of the zone.
	There is a ring on the out of bounds of the Bonus Stage, curiously it has been removed from Sonic 3 & Knuckles.

Carnival Night Zone Palette

Pre-release screenshot	Prototype	In-Game

Applying Launch Base Zone Act 2's underwater palette to Carnival Night Zone results in a color scheme nearly identical to that seen in the Nov 3, 1993 prototype and a screenshot of the level found in pre-release material.

(Source: Sonic Retro)

Knuckles' Theme

Knuckles' theme is just a set of drums that lasts for roughly four seconds, and loops forever. However, at around the 34-second mark is a brief voice sample before the next section of drums. This in and of itself isn't particularly interesting, but it should also be noted that whenever the song plays in-game it's always in scripted events; the song only ever plays for a maximum of 10 seconds or so. The only way to listen to this small sample is to use the sound test, jump just before the bridge collapses in the transition from Angel Island to Hydrocity and land on the piece of land that you fought the boss on and listen to it there, or wait after Knuckles bombs the building near the end of Launch Base Act 1.

100000 Points!

While not technically unused, the circumstances to get this would be extremely difficult at best. Beating a level with a time of 9:59 (1 second from getting a time over) will award the player 100000 points; this also is intentional according to the code.

It would return years later in Sonic Mania.

Changes in Sonic 3 & Knuckles

When locked-on to Sonic & Knuckles, a number of changes were made, either to fix bugs or weird design choices.

Knuckles Art Changes

Sonic the Hedgehog 3	Sonic & Knuckles

The Sonic and Knuckles version of his running sprite ended up being polished to be two pixels shorter and fix some of the leftover torso drawing from Sonic's sprite (though they didn't do a good job, as some tan pixels are still present and the diagonal versions weren't changed at all)

(Source: Sonic 3 Unlocked)

Stages

To do: There are still more differences.

Angel Island Zone

Sonic the Hedgehog 3	Sonic 3 & Knuckles

Upon entering Knuckles' section, you'll be granted with a checkpoint and a multiple sets of spikes. However, in Sonic 3 & Knuckles, the checkpoint and first two set spikes were removed.

• This is the last mention of a checkpoint for this section in Sonic 3, however Sonic 3 & Knuckles proceeds to add two extra later on in the level.

Sonic the Hedgehog 3	Sonic 3 & Knuckles

You can glide onto this wall and climb it if you (somehow) have Knuckles in Sonic 3, but he will never actually stick to the ground at the top once he's there thanks to the invisible GTGT block. This was fixed in Sonic 3 & Knuckles by entirely removing it.

Sonic the Hedgehog 3	Sonic 3 & Knuckles

For a small difficulty modification, the subtype of the spikes were changed and then they got shifted up.

Sonic the Hedgehog 3	Sonic 3 & Knuckles

Sonic 3 & Knuckles adds a path swapper before the boss in order to change Knuckles' priority to be in front of the trees and waterfall.

Hydrocity Zone

Sonic the Hedgehog 3	Sonic 3 & Knuckles

The beginning of Hydrocity Zone Act 2 went through some layout changes that mostly reduced difficulty.

• Both the checkpoint and the rings above it were moved slightly to the left.
• One of the breakable walls before the yellow spring was removed.
• The yellow spring itself that shoots the player closer to the moving wall was replaced with an extra life monitor.
• The area wasn't made completely easier though, as a spike object was added below the second group of three rings.

Marble Garden Zone

Sonic the Hedgehog 3	Sonic 3 & Knuckles

In Sonic 3 & Knuckles, a lot of extra objects were added to this room in Act 2 to prevent Knuckles from taking Sonic and Tails' path; the most important object is the GTGT collision block to prevent Knuckles from climbing the wall and hitting the Relief's eye.

IceCap Zone

• In Act 1, the player is now unable to move after the snow falls on them until they jump out, unlike the standalone 'Sonic 3' where the player can walk freely. This introduced a bug where if Tails carries Sonic out of the snow and crosses a falling barrier, Sonic cannot regain control. If Sonic is then carried onto the slide, the game is softlocked.

Sonic the Hedgehog 3	Sonic 3 & Knuckles

Originally, this was a Sonic & Tails or Tails only path. Sonic 3 & Knuckles added a trampoline so that Sonic can go up there without Tails' help.

Launch Base Zone

Sonic the Hedgehog 3	Sonic 3 & Knuckles

Knuckles' boss arena was edited in Sonic 3 & Knuckles. The most notable difference is the position of the Twin Hammer/Swing’m Spikez boxes.

Sonic the Hedgehog 3	Sonic 3 & Knuckles

This is another notable difficulty change, as this area is very hazardous in Sonic 3. The player would have to avoid breaking the Eggman monitors and enter a room full of spikes to hit the door switch. Sonic 3 & Knuckles moves the switch outside, and turns the room into a bonus room with two Super Ring Monitors. However, hitting the switch will block off the monitors.

Sonic the Hedgehog 3	Sonic 3 & Knuckles

A simple monitor subtype change from a harmful Eggman to a helpful Invincibility.

(Source: Sonic 3 Unlocked)

Regional Differences

Unlike most of the Mega Drive/Genesis Sonic games (including Sonic 3 & Knuckles), Sonic 3 "alone" is region-locked and each region got a separate version.

Japan	America	Europe

One difference between the Western and the Japanese release, like Sonic 2, is the name used for Tails (e.g. Tails for US/Europe, Miles for Japan). However, the only change made here is changing Tails to Miles on the Act results, and it does not change his life counter (his name still says Tails). This was fixed in Sonic 3 & Knuckles.