This needs some investigation. Discuss ideas and findings on the talk page. Specifically: Access and investigate other zones. Try to import art of the respective zones from the original game.
Porting from one system to another can sometimes be tough, as seen with the Game Gear prototype of Sonic the Hedgehog.
There is no Sega logo in the beginning, just like the Master System version.
Act 1 of Green Hill Zone is the only playable stage by normal means. However, Act 2 can be accessed with hacking by using a hex editor and going to offset 155FE and changing C4 to B6. Also, by using level modifier codes, it's possible to play other stages, but most either crash, are empty, or are missing their art. Some, however, are partially playable, with Jungle Zone 2's screen scrolling mechanic still being in the game and Labyrinth Zone's water being fully operational, but none are fully playable.
Proto
Final
The map screen has misplaced points and different smoke graphics. It also uses a similar color palette to the Master System version.
Proto
Final
Sonic is placed further right at the start of the level.
Sonic's palette changes to a darker blue when nearing the signpost; in the final version, he becomes ever so slightly brighter.
Sonic's sprites are nearly identical to the Master System version, with some minor palette alterations.
A strange strip appears at the top of the level briefly. Just a graphical glitch as touching it does nothing.
Proto
Final
The invincibility stars are more similar to the Master System version. The final game has four stars.
Proto
Final
Various things have yet to be added to accommodate the smaller screen size, such as warning signs near spike pits.
The level layout is slightly different compared to the other versions.
Proto
Final
Totem poles have three heads in the prototype, while in the final, they only have two.
Proto
Final
The mountain range has a similar hue to the Master System version.
Proto
Final
The Game Over screen is messed up due to some tile rearrangement.
The credits are still in the ROM. Aside from a messed-up palette and the text not fitting the boxes, it's 100% identical to the Master System version.
Warning sign that would be used in Green Hill act 1, however it is not used in the prototype.
Proto
Final
There is a sign pointing down that is not used in the prototype, although it is used in the final version in act 2 of the Green Hill Zone, its sprites are completely different here, making much more sense with the background.
This palette would be used for objects, with a curious light purple palette as the background. No stage in the game, neither in the Master System version nor in the Game Gear version, has a stage with a similar palette, which makes it a mystery which stage it was supposed to be. This can be found in the ROM from 0x64A8 to 0x64C6.
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The Special Stages can be accessed by modifying the ROM to bypass the reset, and through the same method as the final game (reaching the sign post with 50-99 rings). The game tries to decompress garbage data, which takes a long time, but it has not crashed. The palette used for the special stages is a valid Game Gear palette, which confirms at least a little bit of work went toward making the Special Stages work for the Game Gear at this point:
This palette can be found in the ROM from 0x6488 to 0x64A7. It's slightly different from the Master System palette, though, as the background colour is a dark purple, rather than the Master System's dark blue.
The stages themselves are unbeatable, as most of them trap Sonic in a box he can't get out of at the beginning.
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