Sonic Advance has gone through several changes over its development process. There are several rejected ideas and other things that were left on the cutting room floor. The following details several of these things.
Neo Green Hill Zone
These next five images all have the same differences to the final game; a misaligned HUD with slightly different graphics, different water and clouds in the background and bigger ring sprites.
Sadv-nghz1.jpg
In this screenshot numbers appear top right hand corner, possibly symbolising a debug mode like in the MegaDrive games.
Casino Paradise Zone
The castle in this prototype is a lot duller than in the final, and is of a different shape. In the released game it is much more colourful.
Here the castle is in the centre of the screenshot. In the final it always remains in the top left.
Egg Rocket Zone
Again another misaligned HUD, and this time with some slightly different foreground tiles too.
This area is completely different. The tubes are more rounded with less detail, but the background has more detail. The misaligned HUD and big rings are here too.