Game Secrets:Sonic the Hedgehog 3
From Sonic Retro
Red revolving spheres
This is a spinning mass of red balls, placeable by debug mode in the first part of Angel Island Zone, Act 1. The balls look similar to those appearing in the game's special stage. The object seems to have no apparent purpose. When it is placed, palette problems arise in the level. It can be manipulated with the second controller. Pressing or change the object's size, and move it, and rotate one axis, rotates another axis, and pressing toggles automatic rotation.
Some data for Knuckles seems to be in the game still. Using game genie codes created by LocalH (ASCA-AAHC + ASCA-BA9Y), Knuckles character select and continue icons will appear in game. The level clearing text and the end sign will also have Knuckles graphics. The character you play will still be Sonic.
Lost Eggman Object
An unused Eggman object discovered by Nemesis. It appears to be nothing more than Eggman flying away towards the horizon. Purpose is unknown.
Leftover Sonic 2 Menus
By setting the game's screen mode to $24, you can access the Sonic 2 options menu in Sonic 3! Either use the following patch code:
Or follow the instructions on SCHG How-to:Restore Sonic 2 Menus to Sonic 3.
Unused Surfboard Intro
This animation was found in the Sonic 3 ROM. It's part of an unused intro sequence, in which Sonic surfs onto Angel Island, rather than riding in on the Tornado. The sprites are based on Sonic 2's style, rather than those of the final Sonic 3. This savestate (info) will allow you to see the full sequence in action (thanks to Nemesis).
These sprites were probably used when jumping off the board.
Unused Flying Battery Zone icon
This can be found in both the PC and Mega Drive versions of Sonic 3, and can be viewed by hacking the SRAM for the game to access level slot $04, or by using the PAR codes 00C324:601E and 00C338:6002 to view the icon in a completed game save slot while scrolling through the levels.
True Level Order/Unused Levels
The level select menu reveals what the level order may have looked like had Sonic 3 and Sonic & Knuckles not been split into two separate games. The Sonic 3 levels are arranged the same as they are played in the game, but Flying battery from Sonic & Knuckles can be seen listed in between Carnival Night and IceCap. Following Launch Base two more Sonic & Knuckles levels can be found, Mushroom Hill (which goes by the name Mushroom Valley here), and Sandopolis.
In a commentary found in the Sonic Jam strategy guide it was revealed that the reason IceCap was meant to follow Flying Battery is because Sonic was supposed to break down the door of it, and use that door as a snowboard. It also mentions that Flying Battery was meant as the eighth level, with IceCap being the ninth.
Also, when a level is highlighted, a level icon from Sonic 2 is shown, with the icons appearing in the Sonic 2 order e.g. Angel Island has the Emerald Hill icon, Hydrocity has the Chemical Plant icon, Marble Garden has the Aquatic Ruin icon. Even the special stage has the Sonic 2 special stage icon. It can also be noted that the second '2P VS' level has an icon which resembles the cut 'Hidden Palace' level from Sonic 2.
8th Special Stage
In Sonic 3, there was an 8th Chaos Emerald accessible via a hidden cheat code. The emerald is the same color as the 7th Special Stage, grey. To access it, to go the level select, set the sound test selection to 07, and press + on the "Special Stage 2" selection.
This emerald has no special effect in-game, however, and does not appear on the end of special stage tally in any form other than a score increase.
A map of this special stage is as follows: