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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), Samsung (KR), Tec Toy (BR)
Platform: Genesis
Released in JP: July 26, 1991
Released in US: June 23, 1991
Released in EU: June 23, 1991
Released in KR: 1991
Released in BR: 1994

EnemyIcon.png This game has unused enemies.
GraphicsIcon.png This game has unused graphics.
ItemsIcon.png This game has unused items.
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.

BugsIcon.png This game has a bugs page
PrereleaseIcon.png This game has a prerelease article

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 mascot.

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 on a Japanese console), then hold A and press Start. In the original revision, the level order is different from the order in normal gameplay.

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 region.

International Version

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.

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, B to enable slow motion, or C to enable frame advance.

Japanese Version

When running on a Japanese console, 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.

Unused Sprites


Artwork Description
Sonic1Gen Standair.png
Sonic gulping air. Likely used for the air bubbles found in Labyrinth Zone, as well as Scrap Brain Zone Act 3.
Sonic1Gen Needair.gif
Sonic holding his breath. Possibly used for when the player was close to drowning.
Sonic1Gen Slide.gif
A sliding sprite, similar to those used in Sonic CD.
Sonic1Gen sonicvictorypose.png
Seen in earlier development pictures. Apparently a victory animation used after passing the goal. Slightly modified versions of these sprites would finally see the light of day in Sonic Mania.
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.
Sonic1Gen Falling or shrinking.png
Shrinking, maybe falling, sprites for Sonic. Probably used for a bird's-eye-view section.


These are visible if you fly over the goal in debug mode, 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.

Artwork Description
Sonic1gen Tv eggman.png
A Robotnik monitor. Possibly would have hurt Sonic, like in Sonic 2 and Sonic 3 & Knuckles.
Sonic1gen Tv goggles.png
An image of Sonic's unused goggles, leading some to believe it was originally a power-up.
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 a S on it. This monitor appears in Prototype 510 of Sonic CD, essentially giving the player a speed boost and invincibility.


Green Hill Zone

Artwork Description
Sonic1Gen sonicwreck.gif
This checkered ball, seen in early screenshots, and part of the Green Hill Zone boss in the final. It would have originally been its own object, and would have chased Sonic and crashed through walls that he couldn't break through. The checker ball can still be viewed via debug mode, but cannot be placed.
Sonic1Gen GHZTotem.png
Two faces, possibly from an earlier point in development. Their true palette isn't in the game anymore. 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.
Sonic1Gen Missingghztiles1.gif
Unused tiles from the Green Hill Zone. They would be reused in Green Hill's second act in the 8-bit version. Interestingly, these tiles were used for the Underground segment in Act 2 of the 8-bit version. It is possible that an Underground section was once planned for the 16-bit version as at some point in development.
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 spikeball 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.

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 actived in Marble Zone.

Spring Yard Zone

Artwork Description
Sonic1Gen Letsgo.png
An unused sign present in Spring Yard's tileset, seen in early screenshots.

Labyrinth Zone

Artwork Description
Sonic1gen Burrobot1.png
A Burrobot facing downwards.

Star Light Zone

Artwork Description
Sonic1Gen Light.gif
Sonic1Gen Light2.gif
Unused lights from Star Light Zone.
Sonic1Gen Machine2.gif
Sonic1Gen machinparts.png
Unused machinery scenery.

Final Zone

Artwork Description
Sonic1Gen Robotniklegs1.png
The sprite on the left shows the back parts of the legs of Robotnik's vehicle, which are impossible to see in-game.


Artwork Description
A rosebud with an incorrect palette, which functions like a bumper. This is because both the ending and Special Stage use the same debug item list, resulting in a strange-looking bumper due to different art being used.

Special Stage

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

Artwork Description
Labeled 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 this would have done.


Artwork Name Description
Press Start Button These tiles would have appeared on the title screen, but due to a programming error, they don't. Interestingly, they will appear on Japanese systems after viewing the invisible credits.
Splats the Bunny An unused badnik that seems to have been cut relatively late in development, as both a trading card and a figurine for it were released.
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.

Sonic1MDSonicgoggles Run.gif (How it looks assembled.)

Eggman Explodes These sprites could have been used in the ending, since they show Eggman struggling to stay in the air (and then exploding), presumably only if you attacked Eggman's craft when he tries to escape in Final Zone.
Sonic1Gen BetaExplosion.png
Unused Explosion An unused and quite different explosion, found along with the badnik art. Speculated to be from an earlier version of the game.
Sonic1Gen UnkGrass.png
Unknown Grass A chunk of grass which has no known purpose. Interestingly, it doesn't seem to match with any palette in the game.
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.

Unused Warping Effect


Possibly an earlier method of accessing the Special Stage, this warp effect activates when Sonic runs into the area in which the object is placed. 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 Retro)

Invisible Credits


Credits that are hidden on the Sonic Team Presents screen, and completely unseen in every region outside of Japan. If you 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, enter Down + A + B + C to turn the screen's background to white, making the text visible when the demo finishes. This code does not work in the Sonic Classics version.

The credits translate to:

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

Misplaced Enemies

Sonic1 ghz2 crabmeat.png

In Green Hill Zone, there are multiple misplaced enemies, such as this Crabmeat in Act 2 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.

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 a couple of ways:

  • In 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.
  • In Marble Zone Act 2, if you get a quick start, destroy both Buzz Bombers in one jump, in the same jump make it over the lava, and land, the game may crash with an address error.

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

Other errors exist like a Divide By Zero Error and System Bus error, but they are nearly impossible to see but only one way to see the Divide by Zero error, which is attempting to add the Goggles monitor back into the game.

Revisional Differences

To do:
  • Should we include the differences in the Mega Collection bonus edit (most notably the so-called "spike bug") since it's technically a modified Mega Drive ROM, even though no evidence of official cartridge release exists? Should we also mention the Sonic Jam edition on top of that, which implements the unused skidding effect and includes spin dash/"spike bug" toggle?
  • 3D Sega Classics version differences: Spin Dash, International/Japanese version toggling, Level Select available as toggle in Special menu...

A revision (commonly known as REV01) was silently released, which is more common in the Asian market. Most compilations and re-releases include this altered version. Below are the changes:

  • The game's background deformation and screen drawing routines were given significant overhauls. As a result, the clouds in Green Hill Zone and on the title screen now scroll from right to left (common in most depictions of Green Hill in the series), backgrounds that previously did not have multiple layers of scrolling now do, and the water in Labyrinth Zone/Scrap Brain Zone Act 3 has been given a ripple effect, similar to that of Sonic CD.
  • The level select was rearranged. In the initial release, the Zones were listed in a pre-release order that doesn't represent the final game.
  • There are more changes if the game detects whether it is being played on a Japanese console. Previously, it disabled the Debug Mode but enabled the hidden developer credits - the revision provides new Level Select and Debug Mode codes as well.
  • The points system was slightly altered: extra lives are now gained every 50,000 points, and the final boss now awards 1,000 points in defeat. Previously, extra lives were not acquired upon reaching any particular point total and the final boss awarded no points at all.
  • Minor programming changes of certain properties such as Caterkiller's nuances, lamppost / game over and drowning music exist.
  • Generally, the game code is tighter, more efficient, and removed unnecessary remnants like certain unused sprites.
  • Holding buttons during the attract mode and ending demo sequences will not cause Sonic to miss jumps.

Labyrinth Zone's Extra Ring

Placing single rings is normally an unaesthetic thing to do.

There is one extra ring in Labyrinth Zone Act 1 of Revision 01. After the player presses a button near the two rising platforms, a platform spawns above, something few people know about. It's possible to reach this platform with a well-timed jump, and if the player rides on it, it'll take them to an alternate path which may have an extra ring. With said ring, it is possible to collect 50 rings (and so access the Special Stage) while taking this shortcut.

(Source: Sonic Retro)