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Sonic Chaos (Game Gear)

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Title Screen

Sonic Chaos

Also known as: Sonic & Tails (JP)
Developer: Aspect[1]
Publisher: Sega[1]
Platform: Game Gear
Released in JP: November 19, 1993[1]
Released in US: November 23, 1993[1]
Released in EU: November 25, 1993[1]

AreasIcon.png This game has unused areas.
CodeIcon.png This game has unused code.
DevTextIcon.png This game has hidden development-related text.
GraphicsIcon.png This game has unused graphics.
MusicIcon.png This game has unused music.
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.

ProtoIcon.png This game has a prototype article
DCIcon.png This game has a Data Crystal page

Tails is back as a playable character. Chaotic!

This is also a port of the Master System version.


Read about prototype versions of this game that have been released or dumped.
Prototype Info

Unused Graphics

Artwork Zone Description
SonicChaos GG Unused Title Ring.png
Title Screen Ring Graphics for the title screen's large ring spinning which are loaded on the title screen. This may have been used for a title screen animation. Interestingly, they are not present in the Japanese version.
SonicChaosTurqSpring.png Turquoise Hill Zone A diagonal spring likely intended for the lower parts of the stage.
SonicChaosMegaObjects.png Gigapolis Zone One default spring and four springs in front of some background blocks. There are also spikes meant to be placed in front of background blocks.
SonicChaosMegaHalfPipe.png Gigapolis Zone A left-facing quarter pipe.
SonicChaosSleepObjects.png Sleeping Egg Zone A diagonal spring in front of the checkerboard background tiles, and some default spike graphics.
SonicChaosSleepSlopes.png Sleeping Egg Zone Two different slope types that are unused in this Zone.
SonicChaosMechaObjects.png Mecha Green Hill Zone Diagonal springs and spikes set in front of the mesh background tiles.
Sonic Chaos Unused Mecha Green Hill.png Mecha Green Hill Zone A small unused level piece. A mirrored version of this is used.
SonicChaosAquaObjects.png Aqua Planet Zone Two different spring types, and two background objects.
SonicChaosElecObjects.png Electric Egg Zone Another quarter pipe and spring type.
SonicChaosSpec1Objects.png Special Zone (Type #1) A great number of background pieces intended to be placed with the diagonal background tiles. So are the spikes, which may have had their colors overwritten with the cloud palette.
SonicChaosSpec1HalfPipe.png Special Zone (Type #1) Two more quarter pipe blocks.
SonicChaosSpec2Objects.png Special Zone (Type #2) The second Special Zone tileset has the most unused tiles of any level. This includes the giant rings featured in the other Special Zones, purple and red coral, spikes, and an upward spring. The red blocks are never used in any Special Stage. The presence of these blocks suggests that at one point in development the red Chaos Emerald may have had its own Special Stage.
SonicChaosSpec2Slopes.png Special Zone (Type #2) Both of the Special Zones using this tileset are completely flat. Nevertheless, these slope and quarter pipe tiles are present in the ROM.
(Source: Original TCRF research)

Unused Zones

Sonic Chaos Unused zone.png

Existing in both versions of the game, Zone IDs $06 and $0D have a blank name. In the Game Gear version, they show up as garbled text followed by "ZONE." In the Master System version, they just show up as "ZONE".

Layout-wise, they're a copy of Turquoise Hill with few differences, apart from the occasional graphical glitch:

  • The giant Motobug boss in Act 3 is glitched: after it is attacked once, it stays in its "flashing" palette for the rest of the fight.
  • The HUD doesn't clear correctly before the boss, and continuously loops around the screen until part of it becomes overwritten by the boss graphics.
  • $06 oddly uses the bonus stage music. $0D uses the boss music, but is strangely silent in the Master System version.

Unused Music

Sound Code: 0x8E
Unused jingle of unknown purpose.

Sound Code: 0x9B
While not used here, this track would be recycled (albeit in a lower key) in Sonic Triple Trouble as the Sunset Park boss theme.

Sound Code: 0x83
This is Gigalopolis Zone from the Master System version with a few differences.

To do:
What are those differences? Listening to them, the only one that I could find is pitch.
Game Gear Master System

Unused Text

Like all of Aspect's 8-bit Sonic titles, a basic build string is present at ROM 0xC0:

International Japan
  < Ver1.00 >   
1993/09/01 @SEGA
/Aspect Co.,Ltd 
  < Ver1.01 >   
1993/09/07 @SEGA
/Aspect Co.,Ltd 
(Source: Original TCRF research)

Debugging Features

Error Handler

Sonic Chaos errorhandler.png

Another common feature of Aspect's Sonic games, there's a generic error handler routine at ROM 0x70. If the code at that address somehow executes, the game clears the screen, tries to write the message "ERROR", waits for 3 seconds, and then resets. The game doesn't intentionally jump to this code at any point, and it would be of little use anyway because the message will only be intelligible if an ASCII font is already loaded at VRAM 0x2400 (e.g. on the level select screen).

(Source: Original TCRF research)

Level Select

Sonic Chaos Level Select.png

Press Up, Up, Down, Down, Right, Left, Right, Left, Start at the title screen.

Sound Test

Press Down, Down, Up, Up, Left, Right, Left, Right, 1, 2, Start at the title screen.

The Sonic on this screen is part of an Easter egg: Press Down, Down-Right, Right, 1, and he'll perform a Hadouken!

Regional Differences

Title Screen

International Japan
SonicChaosTitle.png SonicChaosTitleJP.png

The title fonts are different between versions. The larger title screen in the international version moves the "Press Start Button" text down 8 pixels. The international version also gets a trademark to go with its copyright.

Level Titles

International Japan
SonicChaosGigaINT.png SonicChaosGigaJP.png

The title card fonts are completely different between regions. Notably, the international version does not have Act numbers in its font. "Gigalopolis Zone" was shortened to "Gigapolis Zone".

Dr. Robotnik is called "Eggman" in the credits of the Japanese version. Also, the Japanese version uses a combination of Master System and English Game Gear versions' Act 3 layouts. It uses the Master System's layouts for Turquoise Hill Zone and Gigapolis Zone, an altered version of Master System's layout for Sleeping Egg Zone, altered versions of English Game Gear's layouts for Mecha Green Hill Zone and Aqua Planet Zone, and the English Game Gear's layout for Electric Egg Zone.

(Source: Original TCRF research)

Sonic & Tails Kattobi Saisoku Technique

SonicChaos GG KattobiSaisoku.png

The December 1993 editions of Japanese magazines Shogaku Sannensei, Shogaku Yonensei, and Shogaku Rokunensei (Elementary School Grade 3, Grade 4, and Grade 6, respectively) ran a "Sonic & Tails Kattobi Saisoku Technique" (ソニック&ティルスかっとび最速テクニック or "Sonic & Tails Zooming Best Speed Technique") contest in which readers had to perform a time trial of Turquoise Hill Zone, with four categories for Acts 1 and 2 as either Sonic or Tails. Contestants had to finish either Act with a speed rating greater than 700km/h, pause the game after the rating had finished calculating, and press Up + Left + 1 + 2 to display a six-digit hexadecimal code that would be sent in.

This feature only exists in the Japanese Game Gear version, and is removed from all western releases.

(Source: Pengi)