Sonic the Hedgehog (Genesis)

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: September 1991 This game has unused code. This game has unused enemies. This game has unused graphics. This game has unused items. 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

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.

Sub-Pages

Development Info

Prototype Info

Prerelease Info

Bugs

Level Select

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 revision, the level order is different from the order in normal gameplay: Labyrinth and Marble's positions are swapped. 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)

REV00	REV01-REV02
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.

Unused Sprites

Sonic

Artwork	Description
	Sonic gulping air. Likely used for the air bubbles found in Labyrinth Zone, as well as Scrap Brain Zone Act 3. An edited version of this sprite found use as Ray's look up sprite in Sonic Mania Plus.
	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.
	Seen in earlier development pictures. It would be seen as Sonic's jumping sprite after passing a goal. Slightly modified versions of these sprites would finally see the light of day in Sonic Mania, keeping their original purpose. Used in the prototype build.
	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.
	Spin Dash-like sprites. There's a routine which would change Sonic's sprite to one of these, but it's unused, calling it a "Warp" animation. However, a similar animation was made for Mighty's "Hammer Drop" ability in Sonic Mania Plus. Used one of them for an unused code.
	Shrinking, maybe falling, sprites for Sonic. Purpose unknown.
	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 the v0.02 prototype of Sonic CD. Similar unused sprites exist in Sonic the Hedgehog 3 & Knuckles.

Monitors

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. They are all also unused in the prototype.

Artwork	Description
	A Robotnik monitor. It has been seen in the CES video. Possibly would have hurt Sonic, like in Sonic 2 , Sonic 3 & Knuckles, and Sonic Mania.
	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.
	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.
	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.

Zone-Specific

Green Hill Zone

Artwork	Description
	A checkered ball, 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 ball can still be viewed via debug mode, but cannot be placed. 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.
	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.
	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.
	A set of what appears to be earlier versions of the border landscape tiles, Their true palette is unknown.
	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.
	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.

Marble Zone

Artwork	Description
	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. 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. 26 years later, Splats would finally appear in Sonic Mania as one of the enemies in Press Garden Zone, as well as seen broken in the scrap piles in Flying Battery Zone. It's also in the debug mode's object list in Green Hill Zone, much like the 2013 remake.

Spring Yard Zone

Artwork	Description
	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.

Labyrinth Zone

Artwork	Description
	A Burrobot facing downwards. Purpose unknown. Possibly moving on the tile wall.

Star Light Zone

Artwork	Description
	Unused lights from Star Light Zone. These lights were used in the prototype.

Capsule

Artwork	Description
	Unused pieces of a capsule. They are loaded into the data of Robotnik's capsule, and concept art shows extra gadgets attached to the capsule.

Final Zone

At the end of Final Zone after Sonic destroys Robotnik's pistons, 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

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 this would have done. However, a common Japanese pun is used with the letter W, where it would mean “double.”

Misc.

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, and shows in the Brazilian Mega Games 10 version. It can be reactivated by using the code FFD11A:0100. Functions fine in the prototype build.
	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. (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.
	Unknown Grass	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. Interestingly, it doesn't seem to match with any palette in the game. The code remains 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. 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.
	2 By 2 Block	This can be found in tile graphics 2F66E-2F6B6, compressed in the Nemesis format. It is unknown which level this sprite was intended for, but the likely candidates are Green Hill Zone or Marble Zone since the palettes for said levels are the best matches for these graphics.
	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.
	Title Card Period	A period, also intended for the title cards.
	Vertical Small Fireball	A small fireball, similar to the ones the Fire-Breathing Statues shoot in Labyrinth Zone.
	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.
	Sparkle	Sparkles, in a similar style to the invincibility stars.
	Green Hill Zone Log	A version of the rotating spikes in Green Hill Act 3, with the log intact.
	Marble Zone Bricks	Marble Zone's background bricks, separated from the level tiles.

Obscured Sprites

Sonic

Artwork	Description
	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.

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.

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

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)

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 developer credits. 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

Misplaced Objects

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.

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.

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.

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:

• 

  4E

• 

  Using tiles from the prototype.

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

• 

  04

• 

  13

• 

  32

Star Light Zone:

• 

  37

• 

  38

• 

  39

• 

  3A

• 

  3B

• 

  3C

• 

  3D

• 

  3E

• 

  42

• 

  43

• 

  44

• 

  45

• 

  46

• 

  47

• 

  48

• 

  49

• 

  4A

• 

  4B

• 

  4C

• 

  4D

• 

  4E

• 

  4F

• 

  50

Note: Several unused chunks of Star Light Zone still retain the art style used in the prototype and that's because there are several unused chunks, it's possible this level has had many changes throughout its development.

Scrap Brain Zone:

• 

  23

• 

  33

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

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.

ERROR EXCEPTION    
BUS ERROR          
ADDRESS ERROR      
ILLEGAL INSTRUCTION
ZERO DIVIDE        
CHK INSTRUCTION    
TRAPV INSTRUCTION  
PRIVILEGE VIOLATION
TRACE              
LINE 1010 EMULATOR 
LINE 1111 EMULATOR 

Unused Sounds

To do: Check for any more unused sounds, and get better descriptions if possible.

ID: $A5

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.

ID: $A2

ID: $AB

ID: $B8

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 between 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

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

Unused Act Clear Trumpet

Unused	Masa's Demo

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.
• 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 weird routine that logs the collision, suggesting it was meant for a much older version of the 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. This is actually called for, but is stopped by a return command before it starts.
• Some random code near the code to calculate sines.

Revisional Differences

REV01/Japanese Version

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 "TM" symbols in both the SEGA & title screen now disappear.
• The points system was slightly altered: extra lives are now gained every 50,000 points (if it's played on a Japanese console), and the final boss now awards 1,000 points in defeat. Previously, extra lives were not acquired upon reaching any particular point total (which is still the case on US/PAL systems) 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 and unused code.
• Holding buttons during the attract mode and ending demo sequences will not cause Sonic to miss jumps.

Object Layout Differences

• One block was deleted in Spring Yard Zone Act 3. This is because it doesn't even load.
• 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.
• One area in Labyrinth Act 3 was made slightly easier by removing a dangerous obstacle. Specifically, in an underwater section just before the second conveyor belt in the level, there is a series of ball and chains spinning around. The very last one when heading left was removed.
• Some invisible blocks in Scrap Brain Act 1 were moved up slightly, possibly to avoid level-wraps.

(Source: Sonic Retro)

Mega Games 10 Release

This compilation, released only in Brazil in 1997, features an exclusive version of Sonic 1 that happens to enable the unused Press Start Button sprite with the intended code from earlier versions of the game. Other than the title screen change, the game acts exactly like REV00.

Ports and Compilations

Note: The Wii Virtual Console version of the game uses the REV00 ROM.

Mega Play

To do: A user in the Sonic Retro Discord found that the levels that were cut still have data (e.g. Labyrinth Zone's layout data is still present).

This version of the game was ported from console to arcade. The following differences are:

• The "Rings" and "Time" counter in the HUD were switched around.
• The player is now given a set amount of time to finish a stage.
• Extra lives are disabled, whether it's from striking 1-Up monitors or collecting 100 rings.
• Marble Zone, Labyrinth Zone, Scrap Brain Zone Act 3, and Special Stages have all been removed.
  • As a result of the latter being removed, getting the "Good" ending is impossible.
    • The credits and "Try Again" screens were also removed.
  • A rankings screen has been added, which uses the Special Stage theme song.

Sonic Jam

The version of the game included in Sonic Jam has its fair share of differences, including:

• The option to enable the Spin Dash ability from Sonic 2.
• Turning on the above option also changes the behavior of spikes: Previously, spikes would damage Sonic even if he's in the flashing invulnerability state from being hit earlier. This meant, if he landed on a bed of spikes, they would repeatedly damage him until he dies, never giving the player any chance to get away. Now, they follow the behavior of later games, and respect Sonic's invulnerability state.
• Easy and Normal modes, which reduce the difficulty of the game by different measures.
• While skidding after changing direction while running, Sonic leaves small dust clouds behind him, much like in the other Sonic games.
• This version uses CD audio (like Sonic CD), avoiding issues from the original game, like parts of the music being muted by sound effects. However, this also has downsides, such as songs having large pauses before they play (CD seeking times), and Power Sneakers causing the music to restart instead of speeding up from where it already was.
• A lot of sound effects were also altered due to the CD audio, like the ring collecting, skidding to a stop, and spindashing.

This version of the game is also based on REV01, and unlike many other re-releases, is an actual port.

(Source: Sonic Retro)

Sonic Mega Collection

Sonic Mega Collection (and Sonic Mega Collection Plus) include both the REV00 and REV01 versions, as well as a new revision, which features the same spike behavior change as Sonic Jam.

3D Sonic the Hedgehog

This version of Sonic 1 was released on the Nintendo 3DS in 2013, as part of the 3D Classics line of rereleases. It runs on the "Giga Drive", a special Genesis emulator that allows games to take advantage of the 3DS hardware. Changes include:

• Stereoscopic 3D graphics.
• REV00 (labeled as "International") and REV01 (labeled as "Japanese") are both selectable.
• Customizable controls.
• A CRT-style screen filter.
• The Spin Dash.
• The Level Select being unlocked by default.

(Source: https://www.gamesradar.com/segas-3d-classics-3ds-which-one-should-you-buy/)

(Source: Sonic Retro)

(Source: http://sonicresearch.org/community/index.php?threads/3d-sonic-the-hedgehog-1-2-for-the-3ds-hacking-and-discussion.4977/)

Sega Ages Sonic the Hedgehog

A version of Sonic 1 was released for the Nintendo Switch under the Sega Ages banner in 2018. This version is a port of the 3DS rerelease, and as such retains all the changes in that version sans the 3D effects. Additions include:

• The inclusion of the Drop Dash from Sonic Mania. Like the Spin Dash, it can be toggled on and off.
• The addition of "Ring Keeper" mode, a feature from the 3D Classics version of Sonic the Hedgehog 2. This allows players to start each Act with 10 rings, and lose only half of their rings when hit.
• In addition to REV00 and REV01, the Mega Play version of the game is available, marking the first time it has been rereleased.
• A Challenge Mode, in which the player competes for high scores, their best being uploaded to an online leaderboard. There are two modes: Time Attack (in which the player attempts to complete Green Hill Zone Act 1 in the fastest time possible) and Score Attack (in which the player attempts to get the highest score possible in the Mega Play version with only one life).

(Source: Sonic Retro)