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Sonic Chaos (Game Gear)

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Title Screen

Sonic Chaos

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

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.
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

Tails is back as a playable character. Chaotic!

This is also a port of the Master System version.

To do:
Sonic & Tails Demonstration Sample proto as found here.

Unused Graphics

Artwork Zone Description
SonicChaosDebugFont.png General A hexadecimal font. This is loaded into memory (in the Japanese version) after the KM/H has been calculated.
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 however.
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 the game's 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 Zone

Sonic Chaos Unused zone.png Existing in both versions of the game, this zone (ID 06) has a blank name, so it's referred to as simply "ZONE" on the title card. Layout-wise, it's 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.
  • All Acts oddly use the bonus stage music.

Unused Music

To do:
I think the SMS version of the Gigapolis theme is in the Game Gear version, albeit unused in-game and at a lower pitch.

Sound Code: 0x8E
Unused jingle of unknown purpose, though it was likely an early level completion jingle, as it was recycled in Sonic Blast

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.

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)

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.

Press Down, Down/Right, Right, 1 at the Sound Test, and Sonic will perform a Hadouken!

Regional Differences

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.

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".

(Source: Original TCRF research)