Sonic the Hedgehog (Genesis)

This page details one or more prototype versions of Sonic the Hedgehog (Genesis).

Unused ContentUnused graphics, test objects, unfinished enemies, alternate debug displays... this build has it all.

Zone Differences#

Normally, only eight stages are playable without the Level Select. In order: Green Hill Acts 1-3, Marble Acts 1-3, Sparkling Act 1, and Star Light Act 1. By this point, the level order was already changed, and the level select did not reflect this until REV01.

Final Zone isn't available in the Level Select, and levels use their early names. Every Zone contains many differences in the layouts themselves.

Clock Work Zone Act 3 can't be selected, but can be warped to by modifying 68K RAM address FE10 during level load. This can be done using Action Replay code FFFE10:0502.

• It seems to act as a normal Act 3, instead of being effectively "Labyrinth Zone Act 4". Notably, trying to load the level slot that the final Scrap Brain Act 3 occupies (stage 01-03) instead loads a copy of Labyrinth Act 3, indicating that the concept hadn't even been conceived yet at this point in development.
• The stage is completely empty. Sonic just falls forever, due to lethal pits not having been implemented in this stage.

Zone ID 06, which is used in the final game for the ending, hasn't been implemented yet. Trying to access it by modifying the current Zone/Act address will lead to "ZONE ACT. 1" briefly appearing onscreen, followed by the game softlocking because no level data exists for this level slot.

However, the "Act 4" stage ID (03) is also functioning, to varying degrees. Most other levels either contain nothing or an object layout from the first Act of that stage. Notably, Green Hill's "Act 4" slot contains a complete (yet buggy) duplicate of Act 3, heavily implying it was once considered for the ending cutscene before being moved to its own level slot.

Green Hill ZoneYou can't stop the Rock. Labyrinth ZoneThankfully, there's no water here. Marble ZoneThe truth really was out there. Star Light ZoneUnder heavy construction. Sparkling ZoneGood luck. Clock Work ZoneBefore the big Scrap.

Special Stage#

Map	Transition

There's only one Special Stage in this build, with a very simple and unexciting layout, implying that it was only a temporary design.

• Only C can be used to jump.
• Holding down A speeds up the rotation of the stage if it's currently rotating counter-clockwise, or slows down the rotation of the stage if it's currently rotating clockwise.
• Holding down B does the opposite; the stage rotation speeds up if it's currently rotating clockwise, or slows down if otherwise.
• There's no upper cap on the rotation speed, meaning it's possible to hold A or B for long enough to overflow it and have the stage start rotating in the other direction. It's stored as two bytes in address F782 in 68K RAM.
• Start completely stops the rotation of the stage, and doesn't pause the game. Pressing Start again won't restore the previous rotation.
• Only two bumpers are in the entire stage. For some reason, these bumpers push Sonic away with slightly less force than bumpers in regular levels; this is changed in the final game so that they have the same force as regular bumpers.
• A few clusters of rings are present near the start point, but that's all until the player gets to the "Emerald".
• The code to award a Continue when collecting 50 rings is absent. Though, this can't be seen in-game normally as the stage contains less than 50 rings.
• Instead of a Chaos Emerald to collect, an ordinary green block is used as a placeholder, which does nothing when touched.
• There are two different tiles using the textures associated to the "GOAL" tile in the final game:
  • The blue ones (with "GOAL" on them) don't animate or have any function when touched.
  • The red ones (without the text) also don't animate. When touched, they will spin the stage around rapidly before completely stopping all stage rotation. The rotation will remain stopped for 5 seconds (and Sonic's controls locked). After 5 seconds, the Special Stage will be reloaded (respawning any Rings that were collected), the stage rotation will be set back to its starting orientation and speed, and Sonic will respawn at the entrance of the stage without any screen transition in-between. No sound is played when these tiles are touched.
• The player cannot enter object placement mode, despite debug mode being enabled by default in this build, and thus cannot move freely around or place objects of any kind. The code to properly handle entering object placement mode in the Special Stage hasn't been added at this point in development.
• The UP and DOWN tiles - just one of each present in the whole stage - don't animate either. They also don't make any sound when touched.
• The UP tile functions similarly to how it does in the final game. When touched, it will increase the rotation speed of the stage. In the final game, if an UP tile successfully increases the rotation speed of the stage, the tile turns into a DOWN tile; the prototype tries to do a similar thing, as touching the UP tile with increased rotation speed will slow the rotation speed back down to normal. However, the tile does not visually change to a DOWN tile.
  • NOTE: The UP tile's function is extremely easy to break as it is only programmed for the default rotation speed of the level. Increasing or decreasing the rotation speed using the A and B buttons will usually cause the UP tile to not behave as intended. (This bug also technically survived into the final game, but can only be seen when hacking the game to change the default rotation speed of the Special Stage.)
• The DOWN tile behaves as the R tile does in the final game, and reverses the rotation of the stage.
• Collision detection seems to be less refined, with Sonic being able to stick to tiles much easier than in the final game.
• Sonic's jump in this stage is very slightly weaker compared to the final game.
• No score summary is displayed upon exiting the stage.
• The screen fades to black when entering or exiting the Special Stage. The final game uses a special fade to white.

The Special Stage tile IDs are different from that of the final game, and are detailed below:

General Differences#

ROM Header#

The prototype doesn't yet have its own ROM header and instead contains basic template information, with no game name and a date stamp of 1989.JAN, implying that this build was somehow compiled before development had even begun. A reasonable estimation, based on visual cross-checking against UK prerelease coverage of Sonic, places this prototype around February/March 1991.

Pre-Game Content#

Proto	Final

Instead of the well-known Sega logo and iconic "SEGA!" chant, this prototype uses the standard (and silent) palette-cycling Sega logo which opens most other Genesis/Mega Drive games. Unlike in the final game, the logo can be skipped at any point with Start.

The title screen immediately follows; there is no "Sonic Team Presents" card. (At the time, Sega did not normally credit their internal development teams within games.) Unfortunately, adding this screen also created a minor bug. More on that below.

Proto	Final

The prototype's title screen lacks the ™ symbol (not unlike the Japanese release), and features a flashing "Press Start Button" graphic that's absent from the final. It's still present in the game, but because the Sonic Team Presents screen clears half the amount of RAM it should, it never appears onscreen.

During attract mode, BGM doesn't immediately stop when the Sega logo is displayed; the music fades out slowly instead.

Early Demos#

While the demo cycle only shows Acts 1 of Green Hill Zone, Marble Zone, and Sparkling Zone, a demo of Star Light Zone Act 1 is present. It's not normally seen due to the demo cycle having a total of 12 entries, but the demo player code forcing a loop after the sixth. The Special Stage demo also plays in between every stage, rather than being played only at the end of the demo order in the final release. There are no demos present for Labyrinth Zone nor Clock Work Zone.

At first glance, the demos would appear to be broken, as Sonic dies almost immediately by running into enemies or falling off the level. This is because the demo recordings are not only misreferenced, but belong to an earlier compile of the game.

Level Select/Debug Mode#

Level Select and Debug Mode are enabled automatically in this build for testing and preview purposes.

• In debug, holding A and pressing C won't yet go backward in the object list, and instead places the highlighted object regardless.
• The game acknowledges B as a jump input before activating debug mode with the same button. This causes Sonic to jump on the frame before entering debug mode and performing said jump after exiting debug mode. This was fixed for the final version for levels, but was not changed for the Special Stages.
• Spring Yard and Scrap Brain were called Sparkling and Clock Work in this build. These early zone names would end up being used in the Sonic the Hedgehog manga published in the Japanese magazine Mega Drive Fan, which coincided with the release of the game.
• The level select contains Xs next to Star Light Acts 1-3 and Clock Work Act 3. These were likely used for when a stage hasn't been implemented yet (though in this build it's a bit outdated, since Star Light has been implemented).
  • Clock Work Act 3 cannot be selected.
• Pressing B on the Level Select will load up Act "4" of Green Hill (displayed on the title card by a copy of the blue oval graphic replacing the Act number), which suggests that it might have been used to test the ending sequence stage. In the final game, the ending stage instead uses a separate Zone altogether (06).

Proto	Final

Level Transitions#

• Completing Act 1 or 2 of Star Light will send the player to Act 2 or 3 respectively, but clearing Act 3 takes the player to Marble Act 1.
• Beating Clock Work Act 2 will bring the player to Act 3 (which later became Final Zone), and beating Act 3 will bring the player to the Sega screen.

Gameplay#

HUD Differences#

Proto	Final

• As seen in countless prerelease screenshots, the HUD says "Ring" instead of "Rings". The change was made circa the build seen in Shinsaku Soft Video, rather close to the end of development.
  • "Ring" does not flash red when the player has 0 rings, nor does "Time" flash when the clock reaches 9:00.
  • A "Time Over" does not occur when the timer reaches ten minutes. The timer instead loops back to 9:00 indefinitely.
  • During a Game Over, the timer will continue counting up. The final game stops the timer.

Sonic#

• Sonic's jump height is lower. On flat ground, the apex of his jump is 6 pixels lower than in the final.
  • The cause is in one of the global subroutines that handles object movement: in this prototype, gravity takes effect instantly. In the final game, the code was modified to take 1 frame for gravity updates to apply.
• Sonic's deceleration speed is slower, being $40 in the prototype and $80 in the final. The Power Sneakers' deceleration speed is $80 in both this build and the final game, indicating that it was never adjusted to account for the regular deceleration speed's change, resulting in the Power Sneakers deceleration speed and regular deceleration speed being identical in the final.
• Sonic's collision code as a whole is less polished, and features some nuances not present in the final game:
  • Sonic's collision height doesn't change when crouching.
  • Walking/jumping onto objects such as platforms and bridges causes Sonic to lose some of his speed.
  • When hurt, Sonic has no collision with ceilings.
  • Collision is noticeably glitchy, especially when rounding a small incline.
• Sonic doesn't automatically run off the screen after touching the end-of-level signpost and destroying the post-boss Animal Capsule, nor is the player capable of doing so yet. Jumping during the ensuing end-of-level bonus tally causes Sonic to enter the "victory fist pump" pose seen in many prerelease screenshots.

Objects#

To do: Perhaps a comparison video between the proto and final Special Stage ring animations should be added.

• The hidden end-of-Act bonus point markers haven't been implemented yet.
• Special Stage rings haven't been added to the end of Acts 1 and 2 yet. The ring object does exist with full graphics and coding, though it works completely differently from the final game:
  • When Sonic touches the giant ring, instead of instantly disappearing like in the retail version, he instead momentarily gains a "sparkle" effect, after which he then "warps" off of the screen (similarly to the way time travel works in Sonic CD). However, there doesn't seem to be any further coding for it beyond this point in development, as Sonic simply reappears a short distance ahead of the point where he vanished a brief moment after he disappears.
  • Given this behavior, it's probable that the Special Stage rings were originally intended to be placed at ground level just past the signpost instead of up in the air, to give the illusion of Sonic running through the ring and then warping away to the Special Stage. Why this was altered is unknown, but given that remnants of this functionality still exist in the final ROM, it's likely that it was changed fairly late in development.
• Checkpoints are completely absent. In fact, they haven't been coded into the game at all at this point.
• Spikes damage Sonic during all forms of invincibility, including from monitors.
• Some of the animals move slightly slower than in the final game; this affects Pecky (the penguin), Rocky (the seal), and Picky (the pig).

Screens#

• The Continue screen hasn't been implemented yet, likely because there's no normal way to earn Continues in this build.
• The ending cutscenes and credits are completely absent.

Scrolling System#

Vertical positioning is somewhat buggy:

• The camera is much slower when moving vertically, making it easier to outrun the camera (and, in some rare cases, die when doing so) when falling or traveling at high speeds.
• The top and bottom of the stage wrap in every level, even in stages that don't normally utilize vertical wrapping. In stages with lethal pits, this results in the player dying if they travel above the upper stage limit (since Sonic wraps from the top to the bottom of the stage, where the game then thinks he's fallen into a pit).

Debug Mode#

Proto	Final

• Object placement mode ignores camera boundaries. Camera movement also works differently, meaning going to the same coordinates in the same way won't always result in the camera being positioned the same way.

Miscellaneous#

Proto (GHZ)	Final (GHZ)
Proto (MZ)	Final (MZ)

• When a Zone is completed, graphics for the next Zone start decompressing during the fade-out, before the Act transition completes.
• There is no combo bonus for destroying multiple Badniks in a row yet, meaning you will always get a flat rate of 100 points from doing so.
• Onscreen enemies are not cleared after finishing an Act, and can still harm Sonic while the player's score is being tallied. (This can be easily observed in GHZ Act 1.)
• Extra lives are earned at 50 and 100 rings. The ring requirement for extra lives was later doubled to 100 and 200 in the final release.
• BGM and sounds continue while the game is paused.
• The Time Bonus point values awarded upon clearing an Act are different, and overall less generous in comparison to the final game.

Graphical Differences#

Proto	Final

• Title cards have an additional period after "ACT", possibly implying that "ACT" was originally an abbreviation of another, longer word, like "action". This was removed from the final, although the period remains in the data.
• Sonic's sprites are almost identical to the final game, but he lacks his updated "breathing" animation and his extra hurt sprite (used for slides).

Audio#

The snare drum and timpani samples used across all tracks are pitched lower than the final release, as the final game had its DAC driver code rewritten to accommodate the "SEGA!" chant, which resulted in all samples being played at a higher pitch. Curiously, the kick drum had its pitch manually lowered in each track in the final game to compensate for the driver change.

Additionally, the extra life theme seems to cause various minor issues with the sound driver for a brief moment after it finishes playing.

Music#

Sound Effects#

Many, many sound effects have unused voices found in this prototype, all of which were removed in the final.

Changed#

Two sounds have changed between this prototype and the final.

Unused#

There are many unused sounds unique to this prototype, which would go on to be replaced by different sound effects in the final.