Sonic 2 - Sega Game Gear (Prototype)

Compare The Differences After You Played It!

Hidden content

Disabling the AutoDemo

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 - Removed Zone Act 1
• 07 - Removed Zone Act 2
• 08 - Removed 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

Although Zones with IDs 06, 07, and 08 do not work properly, it is possible to access them in another way by changing the values of 0x54B from 00 to 02and changing the value of 0x550 for the Acts.

All of these levels use Green Hills' palette and Sky High's layouts, without the tiles loaded.

Unused Title Card Screen

Setting ROM address 0x30D to 02 will cause an early version of the Title Card to appear! However, it still works and will take you to the level you were programmed to be in. Although this will no longer make the game play like a demo, for some reason Sonic will still be uncontrollable, resulting in him getting stuck in the level, and the AutoDemo music will not play.

It is also possible to access other levels on the Title Card by changing the RAM values: D287 for Zones and D288 for Acts.

Zone:

• 00 - Green Hills Zone
• 01 - Sky High Zone
• 02 - Removed Zone
• 03 - Under Ground Zone

Act:

• 00 - Act 1
• 01 - Act 2
• 02 - Act 3

Build Date

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

Early Title Screen

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. Note that the copyright symbol in the ROM is Line Feed as there is no symbol, so it has been corrected in the image.

It is possible to reactivate this by modifying the addresses: 0x52E from 22 to 02, however due to the graphics of the new title screen it will make your font graphics look all strange, and after a few seconds the game will restart and crash, curiously the palette of this is also loaded.

Error Handler

At 0x70, there is a routine for error handling.

It still works in the game and when activating it a message will appear saying "ERROR" lasting 3 seconds and then the game will restart.

Free movement

Changing byte 64 to 2 will enable the ability to move around a level freely. Once enabled, hold  and press the D-Pad in any direction during gameplay to move Sonic around.