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Proto:Sonic the Hedgehog 2 (Sega Master System, Game Gear)

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This page details one or more prototype versions of Sonic the Hedgehog 2 (Sega Master System, Game Gear).

S2GG AutoDemo-title.png

The Sonic the Hedgehog 2 AutoDemo is a Game Gear EPROM cartridge demonstrating the then-upcoming game, sent to several magazines worldwide for preview purposes. On July 14, 2014, Orengefox from Sonic Retro obtained a copy, and the ROM was released to the public that August.

As the name may suggest, the AutoDemo is not playable and simply plays itself (a tactic Sega would later use to great effect for Sonic Adventure): it starts with a simplified introduction sequence and title screen (much like the final game) before continuing with Sonic running through an early version of Green Hills Zone (complete with loop), gliding through a largely empty Sky High Zone, and briefly riding one of Under Ground Zone's mine carts. Following this, a static "Coming Soon" screen appears and the demo loops from the beginning.

With a special Zone/Act editor and a modified ROM, though, there are more levels than the demo shows!

Much is different from the retail release of Sonic 2, most notably the introduction and title screens and the Green Hills Zone tileset. Tails is also completely missing.

Many early screenshots of the game shown during development are thought to originate from this demo, the primary giveaway being that as gameplay is always the same, the ring and time counts at specific points never change. Furthermore, as the HUD resets at the start of each of the three sections, Sonic is seen using a hang glider mere seconds into play - in the final game, there are no opportunities to use one this early.

(Source: Sonic Retro)
Download.png Download Sonic the Hedgehog 2 (Game Gear AutoDemo)
File: GG_Sonic_2_Auto_Demo_Prototype_(1991-12-05)_Tmr_Sega_CB06_FFFF_v0.00_(JUE)_(!)_(Orengefox).7z (54.3 KB) (info)

Disabling the AutoDemo

To disable the runtime of the AutoDemo, at offset 0x57E replace ​​0B 78 with 00 00. To play the AutoDemo, at offset 0x705 replace ​​AF 32 3C with C3 09 19.

To select a level, at offset 0x550 replace 00 with the desired value ​​below:

  • 00 - Green Hills Zone Act 1
  • 01 - Green Hills Zone Act 2
  • 02 - Green Hills Zone Act 3
  • 03 - Sky High Zone Act 1
  • 04 - Sky High Zone Act 2
  • 05 - Sky High Zone Act 3
  • 06 - Unknown Zone Act 1?
  • 07 - Unknown Zone Act 2?
  • 08 - Unknown Zone Act 3?
  • 09 - Under Ground Zone Act 1
  • 0A - Under Ground Zone Act 2
  • 0B - Under Ground Zone Act 3 (empty)
  • 0C - Intro
  • 0D and 0E - Title Screen

General Differences

  • The Sega screen is different, with no chant.
  • The title screen only features Sonic, who has no animation (but rises from behind the ribbon). Similarly, the opening cutscene merely shows Sonic running.
  • Badniks, bosses, end-of-Act panels, Chaos Emeralds, and monitors are all entirely absent.
  • Only Green Hills, Sky High, and Under Ground have artwork at this point. All other Zones are either not present at this point, or don't have any associated tiles yet.
  • The Zone order is noticeably different from the final: Green Hills and Sky High are the first two, followed by three Acts with no data (trying to load any of these results in a blank screen). Under Ground is played next. Aqua Lake, Gimmick Mountain, Scrambled Egg, and Crystal Egg are not present in this build.
  • Sonic has the idling animation from the Master System version of Sonic 1.
  • A debug camera can be enabled: at offset 0x0064, replace 00 with 02. Press 1, after which you'll be able to move the camera with the D-Pad.


  • A single music track plays throughout the demo. There's no track like it in the final game.
  • The introductory cutscene and the title screen are completely silent.
  • The "rolling down a hill" sound is slightly different, with a cartoonish pitch shift in the end.
  • The sound Sonic makes when falling does not play in the prototype. A similar sound however does exist, unused.
  • The sound of jumping on a spring is the same as the "rolling down a hill" sound.

Level Differences

Green Hills Zone

  • The art is completely different, being more similar to the credits sequence of the final version.
  • Layouts for all three Acts are present, though they only vaguely resemble the final versions.

Sky High Zone

  • Seems to be an earlier version than the one featured in various magazines, and contains no trees or flowers at this point.
  • The lightning flashes are different. Both the rain and the lightning flashes have priority, placing them in front of Sonic and the HUD.
  • The raining Act has a deep pool of opaque water at the bottom that is not present in the final.

Under Ground Zone

  • Contains many tiles that didn't make the cut, including gray bricks and curvy stone pathways.
  • Most of the Zone appears to be made of layered minecart rails. It's likely that the tile definitions were changed to accommodate the minecart rails seen in the demo, and the existing Act layouts were not updated.
  • Act 3 uses alternate and shorter 16×16 block data in which neither the background nor the minecart rails are defined. The way tile definitions are laid out matches perfectly with the layout of the two other Acts (minus the lack of a background). However, since Act 3 is empty, this difference can't be normally seen.
  • A large stone building and what appear to be non-functional horizontal crushers can be seen at the top-right of Act 1. Neither of these elements made it into the final version.
  • The minecart wheel sits above the rail, rather than inside.

Early Level Card


Setting ROM address 0x2BA to 03 will cause an early version of a level card to sometimes appear on resets. It crashes to a black screen after two seconds.

Download.png Download Sonic the Hedgehog 2 (Early Level Card)
File: Sonic_2_Prototype_(Early_Level Card).zip (62.4 KB) (info)

(Source: pwnsrv)

Unused Graphics

Artwork Description
S2ggprotounusedlaugh.gif Sonic laughing in a rather creepy manner, purpose unknown.
S2GGProtoUnusedSonic2.png A sprite of Sonic's waiting animation from the Master System Sonic 1, altered to make him look happy.
S2GGProtoUnusedSonic3.png Likely early versions of the skidding sprites, which are actually closer to those of the Genesis version.
Sonic2SMSEarlyDeathSprite.png Sonic can't die in the prototype, so this isn't used. It's the same as the early death sprite in the final, taken from the Master System Sonic 1.
S2GGProtoMonitor.png No monitors appear in any level, but graphics for them are loaded at the Sega and title screens.
S2GGProtoSwitch.png Switch sprites are located within the Under Ground Zone tileset, but aren't used anywhere.
S2GGProtoSpikes.png Under Ground Zone only has downward-facing spikes at this point, rendering these upward-facing ones unused.
S2GGProtoExplosion.png There's nothing to explode in the prototype, so the explosion tiles that are located within the number/icon sprites are never seen in action.
S2GGProtoDot.png Blocks can't be destroyed in the prototype, leaving this fragment unused.
S2SHtrees.png The trees seen in the final Sky High Zone and in some early screenshots are present in the ROM, but not actually used.
S2GGProtoActScreenFont.png The 16×16 font for the unused level card screen. Only 8 of the 41 characters get used.
(Source: LooneyDude, TheStoneBanana, Kazblox)

Unused Sounds

Sound Effect ID Description
92 A similar sound to the spring/rolling sound, with a different ending.
93 A long explosion noise.
94 A high pitched noise.
95 A shorter version of 94.
96 A beep. Unknown where it could have been used.
97 A low pitched beep.
98 An echoed version of 97.
99 A bumper-like sound.
9A An explosion.
9B A low pitched rising beep.
9C Identical to 99 but with noise. This would later be used in Sonic Drift and Sonic Drift 2 when the player bumps into another racer, albeit slightly slower in both and with different noise in the latter.
9D A higher-pitched rising beep.
9E A small noise beep.
9F A similar sound to 8-bit Sonic 1's jumping noise.
A0 A beep.
A1 Doesn't play anything.
A2 A very high pitched noise.
A3 A similar sound to 8-bit Sonic 1's extra life noise.
A4 A falling noise. A similar sound is used in the final game whenever Sonic falls off of a high platform.
A5 Possibly unknown.
A6 Identical to A5.
A7 A short rising noise.
A8 A spring like sound.
A9 A long beep.
AA A similar noise to the end-of-level count in the final game.
AB Probably unknown.
AC A very high-pitched noise.
AD A sound that constantly rises and falls in pitch.
AE Identical to AB.
AF Another long beep.
(Source: Original TCRF research)


While the build date is present at 0x000C0, it is likely incorrect and marks the start of development, rather than this build's date.

MS SONIC.THE.HEDGEHOG.2 Ver0.00 1991/12/05 Aspect Co.,Ltd

At 0x00869, there's a string of text reading out the title of the game. This may have been used for an early title screen similar to that of a prototype of Sonic Chaos. Interestingly, the text is wider than the Game Gear's resolution, so it may have been intended for Master System builds of the game.

The data loaded into the game's crash handler.


Green Hills

Act 1

Proto Sonic2 autodemo greenhills1.png
Sonic2 final greenhills1.png

Act 2

Sonic2 autodemo greenhills2.png
Sonic2 final greenhills2.png

Act 3

Sonic2 autodemo greenhills3.png
Sonic2 final greenhills3.png

Sky High

Act 1


Act 2


Act 3


Under Ground

Act 1


Act 2