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Sonic the Hedgehog (Genesis)

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Title Screen

Sonic the Hedgehog

Also known as: Baramdori Sonic (KR)
Developer: Sonic Team
Publishers: Sega (JP/US/EU/AU), Samsung (KR), Tec Toy (BR)
Platform: Genesis
Released in JP: July 26, 1991
Released in US: June 11, 1991[1]
Released in EU: June 23, 1991
Released in AU: 1991
Released in KR: 1991
Released in BR: September 1991

CodeIcon.png This game has unused code.
EnemyIcon.png This game has unused enemies.
GraphicsIcon.png This game has unused graphics.
ItemsIcon.png This game has unused items.
SoundIcon.png This game has unused sounds.
DebugIcon.png This game has debugging material.
SoundtestIcon.png This game has a hidden sound test.
LevelSelectIcon.png This game has a hidden level select.
RegionIcon.png This game has regional differences.
Carts.png This game has revisional differences.

DevelopmentIcon.png This game has a development article
ProtoIcon.png This game has a prototype article
PrereleaseIcon.png This game has a prerelease article
BugsIcon.png This game has a bugs page
DCIcon.png This game has a Data Crystal page

Sonic the Hedgehog is more or less the definitive game of the Genesis in the early 1990s and introduced the world to Sega's new blue mascot.


Read about development information and materials for this game.
Development Info
Read about prototype versions of this game that have been released or dumped.
Prototype Info
Read about prerelease information and/or media for this game.
Prerelease Info
Read about notable bugs and errors in this game.
SCD lifeicon leftover.png
Revisional Differences
Sonic the Hedgehog 1... point 3.

Header Space

When playing Sonic the Hedgehog on a emulator, you might have noticed the header has a very large space formatted as:

SONIC THE               HEDGEHOG

This is actually a crude attempt at a line break, which can be seen by setting your hex editor's bytes per row to 16 and looking at 0x00120 inside the ROM.

Level Select

Sonic The Hedgehog Genesis Level Select.png

One of the most well-known codes in gaming history: press Up, Down, Left, Right on the title screen (three Downs if playing the JP version on a Japanese console), then hold A and press Start. In the original release, the level order is different from the order in normal gameplay: Labyrinth and Star Light are earlier than they should be, and Marble and Spring Yard are later. In the Sonic Jam Official Guide, programmer Yuji Naka explained that this is because Labyrinth was supposed to be the second level, but was considered too much of a difficulty spike. This original level order actually showcases the levels getting more and more mechanical in theme, as Sonic gets closer and closer to Robotnik's Factory.

(Source: Sonic Retro)
Original Japan
Green Hill Zone Green Hill Zone
Labyrinth Zone Marble Zone
Marble Zone Spring Yard Zone
Star Light Zone Labyrinth Zone
Spring Yard Zone Star Light Zone
Scrap Brain Zone Scrap Brain Zone
Final Zone Final Zone

Debug Mode

Again, codes for the debug mode vary based on console or game region.

International Version; & Japanese Version on International Hardware

Another well-known code. While Up, C, Down, C, Left, C, Right, C is the most common version, a shorter version is C, C, Up, Down, Left, Right. The main requirement for the code is pressing C twice before the final input of Right. After entering the code, press Start while holding A and continue holding A until Sonic appears in the level. The "Pause Options" (see below) are enabled even if A hasn't been held.

To activate Level Select and Debug Mode, simply enter the Level Select code, push any direction on the D-Pad after the ring sound, then enter the Debug Mode code.

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

  • Invincibility
  • Infinite Time
  • Debug Coordinates (in place of score)
  • Sprite Counter (in place of time)
  • Placement Mode: Press B during gameplay. 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.
  • Pause Options: press A to go back to the title screen, hold B to enable slow motion, or press C to enable frame advance.

Japanese Version on a Japanese system

Here, there are separate codes for the pause options and the rest of the debug features. As usual, they are entered on the title screen and can be combined by interpolating a D-Pad direction between them.

Pause Options:

  • C, C, Up, Down, Down, Down, Left, Right

Debug Mode:

  • C, C, C, C, Up, Down, Down, Down, Left, Right, hold A and press Start

Once enabled, they behave in the same manner as they do when running on non-Japanese systems.

Invisible Credits


Credits that are hidden on the Sonic Team Presents screen, and completely unseen in every region outside of Japan. The credits were added by Yuji Naka in defiance of Sega, which at the time prohibited developers from crediting themselves by their real names (the game's normal staff roll uses aliases instead, as with many Japanese games from the era). If you play the Japanese version and have a Japanese Mega Drive, or switch the region to Japanese, you can use the code C, C, C, C, C, C, Up, Down, Down, Down, Left, Right, which should make a ring noise, then when the demo starts, hold Down + A + B + C to turn the screen's background to white, making the text visible after the Sega splash screen. This code does not work in the Sonic Classics version.

You can also activate this code for the International version if running on Japanese hardware, then it's C, C, C, C, C, C, Up, Down, Left, Right.

If you can't do the above codes, use the Pro Action Replay codes FFFFE3:0001 and FFF604:0072.

The credits translate to:

Position Person
Program Naka Yuuji
Plan Yasuhara Hirokazu
Design Ooshima Naoto
Ishiwatari Jina
Kataoka Rieko
Sound Produce Nakamura Masato
Sound Program Kubota Hiroshi
Makino Yukifumi

Unused Sprites


Artwork Description
Sonic1Gen Standair.png
Sonic gulping for air while standing. Likely used for the air bubbles found in Labyrinth Zone, as well as Scrap Brain Zone Act 3.
Sonic1Gen Gasp.png
Sonic holding his breath, alongside 3 unshaded bubbles. Possibly used for when the player was close to drowning. The face of this sprite would later be used in Sonic Mania, as Sonic is inhaling an air bubble.
Sonic1Gen sonicvictorypose.png
Seen in earlier development pictures. It would be seen as Sonic's jumping sprite after passing a goal. Used in the prototype build.

Modified versions of these sprites would end up being used in Sonic Mania, Sonic the Hedgehog Golf, and albeit still unused, Sonic the Hedgehog (Didj).

Sonic1Gen Slide.gif
A sliding sprite, similar to those used in Sonic CD. Possibly used for sliding a slope or if he was originally skidding. Modified versions of these sprites would later appear in the official "Hedgehog Day Dance Party" video, but not in Sonic Mania itself.
Sonic1Gen Spin.png
Spin Dash-like sprites. There's a routine which would change Sonic's sprite to one of these, but it's unused. However, a similar animation was made for Mighty's "Hammer Drop" ability in Sonic Mania Plus. Judging by the unused code associated with these sprites, it's possible that they were used to create a "squash and stretch" effect when Sonic hit a wall. A special interaction for Sonic hitting walls was present in some early prototypes of Sonic the Hedgehog 2, but was removed in the final game.
Sonic1Gen Falling or shrinking.png
Shrinking, maybe falling, sprites for Sonic. Purpose unknown.
SonictH1 Gen Dead Sprite.png
A black-and-white death sprite, whose purpose is unknown. Possibly would have been used when falling into lava, like in Marble Zone. This is also present, still unused, in Sonic the Hedgehog 2 and Sonic CD. Similar unused sprites exist in Sonic the Hedgehog 3 & Knuckles. Even Sonic Origins Plus contains a similar unused sprite for Amy Rose.


These are visible if you fly over the goal in debug mode or using the level wrapping glitch, as the end-of-level art loading routine isn't executed and the goal art is written over the top of the art for the monitors. They are all also unused in the prototype.

Artwork Description
Sonic1gen Tv eggman.png
A Robotnik monitor. It has been seen in the Computer Chronicles footage. Later used in Sonic 2, Sonic 3 & Knuckles, and Sonic Mania, where it will hurt Sonic; it would have presumably served the same function here.
Sonic1gen Tv goggles.png
An image of Sonic's unused goggles, leading some to believe it was originally a power-up. These become placeable objects in the 2013 remake's debug mode, and are also worn by Sonic during Tails', Mighty's, and Ray's Tornado plane segments in Sonic Mania.
Sonic1Gen Statictv.png
A static monitor, used as a default for invalid object IDs. Scrap Brain Zone contains a number of these (apparently a victim of changing object allocations - the subtypes work perfectly if these are changed to solidity objects) which emit various glitched tiles when broken. They can be placed in Debug Mode, but don't do anything when broken.
Sonic1Gen tv super.png
A monitor with an "S" on it. This monitor appears in Prototype 510 of Sonic CD, essentially giving the player a speed boost and invincibility. In other games it appears in, including this game's 2013 remake, it grants Super/Hyper forms.


Green Hill Zone

Artwork Description
Sonic1Gen sonicwreck.gif
A checkered boulder, seen in early screenshots, and part of the Green Hill Zone boss in the final. As seen in the prototype, it would have originally been its own object that could be pushed around and break through walls that Sonic couldn't and roll through tubes that Sonic could. In certain places it would serve as an obstacle that would chase the player. The checker boulder can still be viewed via debug mode, but cannot be placed. This was used in the prototype build.

It was restored in the 2013 remake, and is also featured in Sonic Mania's debug mode, though only in Green Hill's acts. May also go with the "Wrecking Ball" object below.

Sonic1Gen GHZTotem.png
Two faces, possibly from an earlier point in development. Their graphics are mapped to Sonic's palette in the final, though it could be possible their true palette was removed. They are simply earlier versions of the Green Hill Zone decorations. They can be also seen in the Nick Arcade prototype of Sonic 2 in Green Hill Zone, on the glitched Crabmeats and the Act 3 boss. They are loaded naturally into the RAM addresses FFBAC8 and FFBAD0 and appear a layer in front of the sprites, can be added on Green Hill Zone with these codes, FF5970:0159 happy face, FF5972:015A sad face.
Sonic1Gen Missingghztiles1.gif
A set of unused border-like tiles. Interestingly, These tiles are very similar to the border tiles seen in the 8-bit version's act 2 underground segment. Although still unused in the prototype, these tiles are included in one of its level chunks, which got eventually replaced in the final. These tiles would later appear in Sonic Mania.
Sonic1Gen Missingghztiles2.png
A set of border-like tiles that correspond to a door in the prototype.
The swinging platforms of Green Hill Zone instead carry a wrecking ball when the highest bit of their subtype value is set. The object is fully functional and can hurt Sonic. Technically, the swinging platforms of Marble Zone, Star Light Zone, and the swinging spike ball of Scrap Brain Zone are capable of doing this, too, but the wrecking ball graphics are not loaded, suggesting this feature was only intended for Green Hill Zone. You can see this using PAR codes FFFE06:6B00 + FFD004:1500 during debug mode.
Sonic1Gen UnkBlock GHZPalette.png
A 2x2 block that can be found in tile graphics 2F66E-2F6B6, compressed in the Nemesis format.
Sonic1Gen Unused GHZ Log.png
A version of the rotating spikes in Green Hill Act 3, with the log intact.

Marble Zone

Artwork Description
Sonic1Gen Sidespike.png
A horizontally-oriented spiked chandelier thingy. A fully functional but completely unused object exists for these. Can be added using patch code FFD004:4500 with debug mode active in Marble Zone. Used in the prototype build.
Splats the Bunny, a badnik that seems to have been cut relatively late in development, as both a trading card and a figurine for it were released. No code for Splats exists in the final game, but it does exist in the prototype, where it can be placed in Marble Zone using debug mode, albeit with Marble Zone's palette, which is wrong. It was once meant to appear in Scrap Brain Zone, according to concept art and source code remnants showing its VRAM position. Its original ID was $4F, and similar code would be used for the "Ball" badnik, in the Sonic 2 "August 21st" build.

A functional Splats can be placed via debug mode in the game's 2013 remake, but it wouldn't be until 26 years later in 2017's Sonic Mania when Splats finally got its chance to be fully utilized, sporting a slightly tweaked design as one of the enemies in Press Garden Zone. It can also be seen broken in the scrap piles in Flying Battery Zone. A slightly different variation is also in the debug mode's object list for Green Hill Zone, much like the 2013 remake.

It also appeared in Sonic Superstars.

Sonic1Gen UnkGrass.png
A chunk of grass which has no known purpose. Early concept art shows a mechanic where grass would be differently colored to show the location of hidden spike traps. It doesn't seem to match with any palette, and no code for it exists in the final game and in the available prototype.
Sonic1Gen Unused MZ Bricks.png
Marble Zone's background bricks, separated from the level tiles.

Spring Yard Zone

Artwork Description
Sonic1Gen Letsgo.gif
Leftover from the prototype is an unused sign present in Spring Yard's tileset. As the sign is also unused in the prototype, it was seen only in Concept art; the palette here is from the prototype which made it cycle. Interestingly, it is arranged in a way to work as a sprite.

Labyrinth Zone

Artwork Description
Game Fixed
Sonic1gen Burrobot1.png
Sonic1gen Burrobot fixed.png
An unused sprite of a Burrobot facing downwards. Purpose unknown. Possibly moving on the tile wall. The head is misaligned by 2 pixels in the sprite mapping data. It looks correct in the digitizer files.

Star Light Zone

Artwork Description In-Game
Sonic1Gen Light.gif
Sonic1Gen Light2.gif
Unused lights from Star Light Zone. These lights were used in the prototype.
Proto Sonic1Gen Light.png

Unused Egg Capsule Machinery

Sonic1Gen Machine2.gif Sonic1Gen machinparts.png

Unused pieces of the post-boss Egg Capsule. The code that sets up the main capsule has two unused parts - One sets routine 4 and loads sprite frame 0x03, the other sets routine 5 and loads frame 0x05. Frame 0x03 points to a mapping frame for the button, but frame 0x05 is the unused smaller piece of the capsule, implying this wasn't intentional. Unfortunately, both the routines they call point to the explosion handler for this object, implying the routines for it were removed.

Had it remained implemented, it likely would have been attached from the back of the capsule, as detailed in a piece of concept art for Eggman.

Sonic1 EggmanCapsule UnusedMockup.png

The bottom half of the larger unused bit would go on to be used in Final Zone, albeit as a different art file entirely.

Final Zone

At the end of Final Zone after Sonic destroys the Egg Crusher, Robotnik quickly attempts to fly away with his Egg Mobile. Before he takes off, the Egg Mobile has a pair of bird legs that retract. The legs are actually taller in their raw graphics (revealing a mechanical knee), as the legs are cut off in-game.

Raw Graphics In-Game
Sonic1 robotnikfeetgraphics.png Sonic1 robotnikfeetingame.png

Special Stage

These can be seen in normal gameplay by falling out of a Special Stage using debug mode.

Artwork Description
Labelled as Zones 1-6, possibly used to mark which Special Stage you were in.
A 1-up icon. This is mentioned and shown in the game's manual but doesn't appear in-game outside of the aforementioned out-of-bounds area. It is actually fully coded and functional, and collecting it will grant you an extra life. The icon disappears like a ring when touched.
A W block. It's unknown what specifically it would have done, but source symbols left over in the Sonic 2 Nick Arcade prototype suggest it had to do with warping, as it is referred to as "warp."


Artwork Name Description
Press Start Button This text was meant to appear on the title screen, but was disabled due to a programming error involving the Sonic Team Presents screen. Interestingly, it will appear on Japanese systems after viewing the invisible credits (since performing that disables the Sonic Team presents screen), and is restored in the Brazilian Mega Games 10 version. It can be reactivated by using the code FFD11A:0100. This functions as intended in the prototype. The basic function of this text is fully restored in the 2013 remake, though it's modified to say "TOUCH TO START". It also says "PRESS BUTTON" when a controller is plugged in, and in Sonic Origins.
Sonic1 MD UnusedLevelSelect Characters.png
Level Select Characters Characters found within the 8x8 font which isn't included in any of the strings. This interestingly features three special characters. "W" is used in the prototype.
Goggles Unused sprites for goggles, which would have been placed over Sonic. It was most likely supposed to come from opening the respective Goggles Monitor. These were later used in Sonic Mania for when Sonic is piloting the Tornado when playing as Tails, Mighty, or Ray.

Sonic1MDSonicgoggles Run.gif (How it looks assembled.)

Robotnik Explodes These sprites could have been used in the ending, since they show Robotnik struggling to stay in the air (and then exploding), presumably only if you attacked Robotnik's craft when he tries to escape in Final Zone.
Unused Switch An unused frame of the switch sprite. When bit 5 of a switch's subtype is set, it makes the object flash, using this sprite. In Labyrinth Zone, this sprite's data is partially overwritten by the cork sprite in VRAM. Marble Zone's switch has no equivalent sprite. This switch was used to close a door, it is present in the prototype in a set of objects without reference from Sparkling Zone 1.
Title Card K The only letter meant for the title cards that went unused after the prototype, since nothing calls for any use of it. It would've been used for Sparkling and Clock Work, but they were respectively renamed to Spring Yard and Scrap Brain.
Sonic1gen titlecardperiod.png
Title Card Period A period, also intended for the title cards.
Sonic1Proto MD Sprite UnusedFlame.png
Vertical Small Fireball A small fireball, similar to the ones shot out by the gargoyle statues in Labyrinth Zone.
Sonic1Gen BetaExplosion.png
Ballhog Bomb Explosion An unused and quite different explosion, meant for the scrapped front-facing Ballhog badnik's bomb and Buzz Bomber badnik's unused exploding projectile routine. The explosion, and the Ballhog badnik itself can be found in the prototype build, albeit still unused.
Proto Sonic The Hedgehog Genesis smoke puff.png
Large Smoke Puffs Some sort of smoke or dust. This is loaded in VRAM within the prototype, where the final game's checkpoint graphics would've been found.
Sonic 1 Prototype Sparkle.png
Sparkle Sparkles, in a similar style to the invincibility stars.

Obscured Sprites

Artwork Description
Sonic1MD LowerHalf.png
The lower half of Sonic's title screen animation are hidden behind the SONIC THE HEDGEHOG ribbon, making these go obscured. These are actually leftovers from the genga (key animation) sketches, seen here. They can, however, be seen in numerous early emulations of the game (Including the official Sega Smash Pack Volume 1 for the Dreamcast), which incorrectly render Sonic in front of the logo.
Sonic1MD CorruptRollerCorrected.png
Due to a level art list error, one of the Roller sprites are overwritten with Caterkiller art. Sonic1MD CorruptRoller.png
This causes the full graphic to never be seen in-game.
Sonic1MD End Shadow.png
The "END" graphics where Eggman jumps on the logo has its shadow graphics below separated from the rest of the text.
Sonic1MD SeparatedContinueSonic.png
Sonic's hand on the continue screen is separated from the main sprite. Oddly, it's misplaced one pixel to the right.
Sonic1MD EggmanLegs.png
Eggman's legs in his crouch and jump frames are obscured by his main body sprite.

Zone Leftovers

Zone ID 06, Act ID 00 (Act 1) and Act ID 01 (Act 2) are used for the ending sequence (good ending and bad ending respectively) in the final game, however, Zone 06 exhibits some odd behavior when played as a regular level. It plays the Final Zone music, and doesn't have an act number on the title card (which just says "Zone"). This isn't due to reading garbage data either, this level is specifically assigned these music and properties. The collision has some problems, and the graphics are messed up too.

Act ID 00 (Act 1) spawns Sonic where he normally is during the good ending, while Act ID 01 (Act 2) spawns Sonic where he normally is during the bad ending. Act ID 02 (Act 3) is unused and completely empty, resulting in Sonic falling to his death.

Unused Warping Effect

An example of the warping in effect


This was used in the prototype when running into a giant ring; Sonic disappears as he runs into it, and a warping noise plays. Sonic then reappears a few seconds later, likely as a method of testing the object.

(Source: Sonic Database)
(Sprite Ripping: Cioss)

Misplaced Objects

S1 GHZ1 Misplaced motobug.png

In Green Hill Zone Act 1, a Motobug is suspended above an abyss near the first group of spikes. It is quickly erased from memory because there is no collision area for it to spawn on. A stage planning sheet reveals that a Motobug was once placed at the top of the hill immediately past the misplaced Motobug, in front of the spring, so perhaps this is a remnant of that early design.

Sonic1 ghz2 crabmeat.png

Green Hill Zone Act 2 has multiple misplaced enemies, such as this Crabmeat at coordinates 10D0,0370, under the section with the moving pillars and spikes just before the checkpoint. They cannot be seen in gameplay, as they're always placed such that they instantly fall into the abyss and unload. The Crabmeat is particularly amusing in that it's already below the level of the screen.

S1 GHZ3 Misplaced stone.png

A stone can be found below the boundaries of the map in Green Hill Zone Act 3, near the boss fight. It is impossible to reach it without the use of debug mode. You can also find a Buzz Bomber that is impossible to reach at coordinates 21B0,0000.

In Labyrinth Zone Act 1, there is a group of spikes buried in 12D3,0675. It is impossible to see them because they are out of bounds and the foreground tiles are in a layer above the sprites. For some reason, the spikes are located at the same coordinate in act 3.

Act 1 Act 3
S1 LZ1 Misplaced spikes.png
S1 LZ3 spikes.png

Unused Level Chunks

To do:
  • Identify whether there are differences or whether they are just unused copies.
  • Pay attention to the chunks carefully to see them if they're in the prototype.

Labyrinth Zone:

Marble Zone:
These have been unused since the prototype, that or they were made but never used.

Star Light Zone:

All of these chunks are used in the prototype. The final rendition of Star Light Zone does not require as many unique chunks as the layout in the prototype does, leaving many leftover chunks that retain the prototype Star Light Zone art style. In addition, while the prototype does use the background chunks that are seen here, the final game has copies of these chunks in earlier chunk slots and uses those slots rather than the ones here.

Scrap Brain Zone:

Chunk 33 is used once in the prototype, near the end of Act 1. Chunk 23 was also used in the prototype's Act 2, but it had a completely different design there.

Unused 2x2 Tiles

To do:
Check the tiles that are in the prototype.

All tiles loaded into VRAM are organized by spreadsheet at the RAM address FFB000, where IDs are created for each line representing 2x2 chunks of VRAM graphics. Address FF0000 is in charge of adding mirroring and collision to these tiles, creating 16x16 chunks.

In all, there are 255 chunks created from FF0000. To add these chunks, add the IDs below in the format (0x xx) after FF0000 and search for the chunk ID 01 in the level data. Through this method, it's possible to see some of the unused graphics referenced above.

Zone Image IDs
Green Hill Zone
Plane A Low
Plane A High
006, 187, 199, 19A, 00C, 00E, 017, 018, 022, 028, 02B, 02C, 044, 048, 049, 055

057, 058, 059, 05C, 05E, 086, 087, 0BD, 0BE, 0F4, 0F5, 0F7, 146, 159, 15A, 161

Marble Zone
Plane A Low
058, 059, 05A, 05B, 065, 069, 06A, 06B, 06C, 08A, 08C, 094

095, 096, 097, 09A, 09B, 09D, 09E, 0A3, 0A4, 0B7, 0B8, 0B9, 0BA, 0BB, 0BC, 0C8
0C9, 0CA, 0CB, 0CC, 0CD, 0CE, 0D1, 0D2, 0D3, 0D8, 0EE, 11A, 11B, 130, 143, 144
145, 146, 147, 149, 14A, 14B, 14C, 170, 171, 172, 173

Spring Yard Zone
Plane A Low
01C, 01D, 02B, 06A, 06B, 072, 08B, 08D, 0AC, 0BA, 0BB, 0D2, 0DD, 0F6, 0FB, 104

10C, 10D, 16F, 171, 191, 192, 197, 1A5, 1A6, 1A9

Tiles 0F6, 16F, and 171 were all used in the prototype for background elements.

Labyrinth Zone
Plane A High
03C, 03D, 04F

The first two tiles were used in the prototype, which lacked the water slides, and used these in their place.

Star Light Zone
Plane A Low
Plane A High

018, 019, 01A, 01B, 01C, 01D, 01E, 01F, 021, 022, 023, 024, 025, 026, 027, 028
029, 02A, 02B, 02C, 02D, 02E, 02F, 031, 032, 033, 034, 035, 036, 037, 038, 039
081, 085, 086, 088, 089, 0F7, 0FA, 103, 109, 10A, 10B, 10C, 10D, 10E, 10F, 110
111, 112, 113, 114, 117, 11A, 11D, 11E, 11F, 121, 124, 125, 128, 129, 13B, 13C
13D, 13E, 140, 141, 186, 187, 188, 198, 19B

Tiles 140 and 141 are used in the prototype for an early rendition of the fireball launcher obstacle.

Scrap Brain Zone
Plane A Low
Plane A High
01A, 01B, 01C, 01D, 029, 02A, 034, 03E, 047, 048, 06A, 074, 07B, 085, 086, 0C0

0D2, 0DC, 0EA, 128, 132, 13F, 141, 16C, 172, 173, 17C, 182, 188, 189, 223, 224

Some of the tiles shown here are in the prototype including small wheel, zig zag, and tightrope tiles.

Exception Handler

StH (Genesis)-Exception Handler.png

The game contains a very basic error handler. In the event a 68000 exception occurs (e.g. a bug causes the game to crash), the game will stop and print some basic information to the screen. This can be triggered in the first two acts of Labyrinth Zone. If the camera is panned down at the moment the results screen is about to appear at the end of the first two Acts, the game may crash with an illegal instruction exception.

These are best performed on an actual console, as the error handler does not work properly in some emulators.

While the error handler has text for most of the defined 68000 exceptions, very few of them are likely to show up during normal gameplay, as many of them are assigned as placeholders.

A way to get out of error messages is by pushing C, but sometimes it won't work properly and will either show another error message, or lead to the game freezing entirely.

A complete list of the game's error messages (which are shown below) can be found at hex value 000004E0.

BUS ERROR          

Unused Sounds

Sound ID Sound Description
This sound effect was used for when the earlier Ballhog bombs exploded while hitting the ground, and when the Buzzbomber missile made contact with Sonic. In the released prototype, the sound can only be heard when the ballhog bombs hit the ground.
These sounds are similar to the spike sounds in the final game.

Unused Music Sequences

In the game, there exists some unused sequences for music, most of which are either a little or very different than the final version.

Unused Credits Sequence

Unused Masa's Demo

This unused sequence sounds almost exactly like the track from Masato's demos titled Theme of SONIC THE HEDGEHOG Demo which has many major differences from the final version, one of which there being that an extra note is being played.

Unused Boss Bass

Unused Masa's Demo Final

The unused bass instrument is similar to the Masa Demo version.

Unused Act Clear Trumpet

Unused Masa's Demo Final

The unused instrument makes this sound near identical to the Masa Demo version as well.

Unused Code

Sonic 1 has quite a bit of unused code, most of which were meant for a much older version of the game:

  • An unused routine to squish Sonic, which played the unused "warping" animations shown above. When this routine is enabled, it activates when Sonic is near a wall, causing him to stick in place, as if he was hanging onto the wall. It is completely unknown what this was meant for.
  • Sonic in the Special Stages has some leftover code that would've limited his jump height, just like the Sonic in normal stages. This does not exist in the prototype.
  • There's a third music queue that's never called for. Even if it was, a bug in the sound driver prevents it from working.
  • Code to record the demo inputs.
  • A routine that converts the collision from a 'bitmap'-like format to the one used in-game. Interestingly, this was altered in the Sonic 2 Nick Arcade Prototype so it would convert Green Hill's collision to work with the new collision table, though it doesn't work since both variations would require a special development cartridge that could overwrite itself.
    • Interestingly, a remnant of the data it was meant to convert can be found in the J2ME port under blkcol.bct.
  • A routine to calculate a square root; this particular code was removed in the Japanese version.
  • Alternate code for the invincibility stars trailing behind, making them trail behind a bit less.

Unused Palettes

Palette Description
Sonic1 MD Marble Cycle.png
A palette cycle for Marble Zone's lava and torches in the background. It doesn't work very well when applied though - it may have been intended for an older iteration of the Zone's artwork, as prerelease screenshots show that the look of the lava changed significantly during development.
Sonic1 Unused SpecialStage Cycle.png
Alternate background palettes for the special stages.