Sonic the Hedgehog (Genesis)/Revisional Differences

This is a sub-page of Sonic the Hedgehog (Genesis).

Revision 01

Often erroneously referred to as 'the Japanese version' despite not being exclusive to Japan, most compilations and re-releases include this updated version. The original release's ROM header labels itself as revision '00', while this one is labelled revision '01'. 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 and the third act of Scrap Brain Zone has been given a ripple effect, similar to that of Sonic CD.
• The level select screen was rearranged. In the initial release, the Zones were listed in a pre-release order that doesn't represent the final game, with Green Hill (Zone 1) and Scrap Brain (Zone 6) being the only Zones to retain their original positions. The level order for the second through fifth zones is as follows:

Revision 00	Revision 01
Labyrinth Zone	Marble Zone
Marble Zone	Spring Yard Zone
Star Light Zone	Labyrinth Zone
Spring Yard Zone	Star Light Zone

• There are more changes if the game detects 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 and title screens now disappear.
• The points system was slightly altered: extra lives are now gained every 50,000 points (only if 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 were made to certain objects:
  • The Caterkiller no longer messes with the program stack, likely to prevent an obscure crash.
  • The game over now resets the time at the last lamppost.
  • The monitor contents object can no longer interrupt the drowning music.
  • Marble Zone's bricks had a single line changed relating to collision, although what it does is unknown. The object is also now programmed to only display when fully initialized, although many other problematic objects remain unfixed.
  • Object 56 (used for both floating blocks in SLZ/SYZ and large doors in LZ) subtype 36 is specifically programmed to not be deleted when off-screen. This object also no longer displays before initalizing.
• 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.
• The ending now freezes on Sonic for 5 seconds instead of 2; the debug list (also used for the Special Stages) were also altered, removing all the animals and bumper.
• The routine that handles object collision was altered; if Sonic has died, it now completely ignores all checks for whether or not he is pushing, likely to prevent his walking animation from playing if he died while pushing an object.

To do: Rip and compare the backgrounds.

• Marble Zone, Spring Yard Zone, and Scrap Brain Zone all had their backgrounds re-arranged; Marble and Scrap Brain both had their clouds re-arranged, while Spring Yard's entire background layout was redone to prevent parts from appearing "cut-off" thanks to its new scrolling routine.

Object Layout Differences

• One block was added in Spring Yard Zone Act 3 to make sure that, after pressing a button, another block remains at its final position.
• There is one extra ring in Labyrinth Zone Act 1. 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.
• A few nearby areas in Labyrinth Act 3, close to the second conveyor belt in the level, were made easier by removing a few enemies (two Jaws and an Orbinaut) and a series of ball and chains spinning around (specifically, the very last one when heading left).
• 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 (with a limited Asian release) in 1997, features an exclusive version of Sonic the Hedgehog that happens to enable the unused "Press Start Button" sprite. All other features are the same as in the original release.

Ports and Compilations

Note: The Wii Virtual Console release uses the original 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).

The Mega Play arcade version is a port of the Genesis game with some differences:

• The "Rings" and "Time" counter in the HUD were switched around.
• The timer now counts down instead of up. The amount of time you're given to clear the level varies on the level. Getting a Time Over causes the player to lose a life and return to the last checkpoint with the timer cleared, as in the retail game.
• The player begins the game with three lives as normal, but it's impossible to gain extra lives, 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 Special Stages being removed, the criteria to getting the good ending has been changed from getting all the Chaos Emeralds to beating the game deathless.
    • The credits and bad ending (the "TRY AGAIN" screen) were also removed.
  • A high score ranking screen has been added, which uses the Special Stage music.

Sonic Classics

To do: Get a visual comparison between the regular cycling palette and the corrupted one.

The version of Sonic 1 included within Sonic Classics is bit-for-bit identical to the original ROM (barring the different ROM addresses), but introduces a bug where Scrap Brain's palette cycling is bugged. This is due to the game being stored at 2 MB in the Sonic Classics ROM, however Scrap Brain's palette cycling pointers only support up to 1 MB. As a result, the game pulls the new palette entries from junk data.

Sonic Jam

To do: Easy Mode removes some levels. Do those levels have Easy Mode data? If so, POTENTIALLY document differences.

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 XA ADPCM audio instead of sequenced music, 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 different sound chip the Saturn has, such as collecting rings, skidding to a stop, and spindashing.
• Green Hill Act 1's camera events were changed to immediately set the bottom boundary of the latter section of the stage, instead of letting it gradually shift towards it. This was done to prevent Sonic from going past the bottom boundary too quickly as it shifted if he was going too fast. With the Spin Dash added, it was made much easier to trigger that issue while going down the roll tunnels.
• Some objects had their code modified:
  • The spikes object had an additional subtype added. It's just the regular 3 spike group facing up subtype, but only the leftmost spike is visible. It was used for the platforming section in Green Hill Act 2 with the Normal difficulty (and also Easy difficulty) to artificially extend the widths of the beds of spikes.
  • The platform object also had an additional subtype added. It's just the regular stationary subtype, but its collision width was extended. It's also used in the platforming section in Green Hill Act 2, placed under the larger platforms that move up and down.
  • The monitor's collision code was modified to allow Sonic to Spin Dash next to it and break it upon unleashing the Spin Dash. The original code would've prevented Sonic from doing that.
  • The player's Caterkiller piece collision code added an extra check that checks if the head of the Caterkiller was destroyed. This was done to fix Sonic being able to speed into a Caterkiller and still get hit by the body, even if the head was destroyed.

(Source: Sonic Retro)

This version of the game is also based on revision 01, and unlike many other re-releases, it is an actual port.

Sonic Mega Collection

Sonic Mega Collection (and Sonic Mega Collection Plus) include both the original revision 00 and revision 01, as well as a new revision which features the same spike behavior change as Sonic Jam. Unlike Sonic Jam, however, this was accomplished by, rather hackishly, overwriting part of the original spike hurt code with a check for Sonic's hurt timer, and then a jump to a backup of the code originally found at that location, now relocated to a part of the header near the end of the 68K address vectors that was unlikely to ever be read. This seems to imply that the revision found in Sonic Mega Collection and Sonic Mega Collection Plus had been made by taking a Sonic 1 ROM and editing it with a hex editor to change the spike behaviour.

3D Sonic The Hedgehog

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.
• Both revisions 00 and 01 are selectable (and are confusingly labeled as "International" and "Japanese" respectively, despite both versions being released in both markets).
• 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

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 except 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 2. This allows players to start each Act with 10 rings, and lose only half of their rings when hit.
• In addition to both revision 00 and 01, the Mega Play version 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 Act 1 of Green Hill Zone 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)