Early designs of Shadow, at the time named Terios.
Examples:
- A rumored earlier premise of the story was Shadow and Rouge were from another dimension and destroying the world, and it would be up to Sonic to stop them. This concept seems to be a proto version of what would become Sonic Rush.
- Shadow’s original name was "Terios", which means "reflection of" (but in promotional material his name was Dark Sonic), along with several early designs for Shadow, some can be found on the page image above, show him missing an eye, and at one point, he had black eyes with a singular red pupil, Some designs with a more muscular body, a design with sunglasses and a head visor, a design where he has hair on his forehead, one with a scratched out eye wearing an ominous cape and holds a knife, and some designs similar enough to Sonic that the game's plot point of Mistaken Identity is much more justifiable. Possibly scrapped due to being too scary or the idea of rendering one eye on Shadow's conjoined eye to not look believable or possible with the technical limitations. The scarred eye version would later be added as a skin for Shadow in Shadow Generations.
- And before that, Rouge had a completely different name. You'll probably never guess what it is. Here's a hint: it ended up being given to another character. It's Shadow. Yes, you read that right, the Ultimate Life Form's name was originally meant to go to Rouge
. Also, Another early name for Rouge’s was "Nails", possibly to rhyme with Tailsnote and/or to contrast with Knuckles. - Sonic was originally going to wear his classic shoes before the deal with SOAP to have him wear a custom version of their shoes was inked. The demo released along with Phantasy Star Online still has these shoes, as well as in Sonic's first scene by mistake in the Dreamcast version, before it switches to his SOAP shoes on the shot of him on the helicopter's wing.
- Early concept art shows that Sonic would have been in Radical Highway instead of Shadow—the only time Sonic is at that level is in the intro and the multiplayer. The concept art also shows a different design for the G.U.N. Robots.
- The Chao Gardens are rife with unused assets, particularly in Battle. As a result of the HD releases lacking access to the GBA-exclusive Tiny Chao Garden, more of these things are unavailable in them.
- While the Smart Fruit was available in the Dreamcast version, it is one of the three foods unavailable in Battle. It raises the hidden Intelligence and Luck stats of a Chao, while the Grapes, which raise Stamina and Luck, have a broken model that renders only the texture of the stem; and the Mint Candy provides insane amounts of stat experience but causes erratic stat increases upon leveling up that don't often match the amount given by a Chao's grade for a particular stat. The Peace and Energy Fruits from the Dreamcast version and most of the Dreamcast version tree seeds, all exclusive to Chao Adventure 2, were completely removed from Battle.
- Two unused shades of blue, dubbed dark blue and powder blue by fans, are present within Battle's data. They come in both monotone and two-tone varieties, but appear to lack egg textures. In regards to textures, Battle made the Moon texture (exclusive to the game's now-defunct website which allowed you to purchase .vmi files of special Chao colors from the Black Market page when using the Dreamcast's browser) unavailable while adding four new and also unused Chao textures— Glass, a gray glasslike gradient, two dull blue gradient textures called Metal in their files, and the texture for the Pearl Race medal from Sonic Adventure. The Dreamcast version also has unused metal textures, but these appear to differ from Battle's. Additionally, the old jewel textures used in the Dreamcast version are located in a separate folder.
- In the Dreamcast version, the Kid's Troops Chao Rangers use modified versions of all of the jewel textures sans silver, in which the textures and gleams are darker than usual. These variants can be obtained through hacking. In Battle, they just use the shiny colors instead.
- A partially-programmed pacifier was a headgear that appears to have been supposed to place a pacifier over a Chao's mouth when given to them. However, like all headgear, it just replaces a Chao's head model(s) with that of the pacifier and creates a weird effect in which the Chao appears to be headless.
- Every Chao color except for the shiny jewel ones has an egg texture, even the colors exclusive to breeding like color two tones— an egg created as a result of breeding normally generates with the normal egg texture. They all have dummy data that allows them to be purchased from the Black Market in egg or shell form should they be hacked in.
- As mentioned above, the HD rereleases rendered the jewel colors and Tiny Chao Garden-exclusive fruits unavailable. In addition, the texture system was not properly ported and renders both the usual shiny two-tone and shiny jewel colors unavailable as a result. Bred shiny two-tones render with ridiculously bright textures with little of the original colors visible.
- Some leftover data from the Dreamcast version shows that originally, there was a Chao Playground and Chao Library planned. The Library would allow you to create new files for the Chao Adventure VMU game, but the Playground's function is unknown. Geometry data for them still exists in the PC version.
- The Hero and Dark Gardens would have had three toys each like the normal Chao Garden if the pianos were implemented. It's likely that they would have been given as prizes for winning part of the Hero and Dark Races, but unknown if said races were originally going to have more than four levels. The Hero Garden piano would have a Chao play a piano rendition of the Chao Garden theme or Sonic Advance's multiplayer waiting theme, while the Dark Garden organ would produce an organ rendition of the Tiny Chao Garden music.
- For a long time, it was believed that the Knuckles and Amy Chao were unavailable legally and that the Tails Chao was only available through a special mission in Phantasy Star Online - prior to Battle, the Knuckles Chao was an Urban Legend of Zelda. In reality, all three official character Chao are available on the Gamecube version of Battle through an obscure Japanese demo disc released in 2003— the Tails Chao is technically Neutral, the Knuckles Chao is Hero and the Amy Chao is Dark. All three are unobtainable in the HD versions.
- Unused text for the Chao Health Center indicates that Amy was at one point able to access the Chao World; she is the only multiplayer character to have such text in the game's files. Since the Chao World can only be accessed in singleplayer, this seems to indicate she may have initially been planned to be playable in the campaign at some point.
- In Battle, after getting an A-Rank on Green Hill Zone, Super Shadow and Super Sonic would have been unlocked in two-player mode. All that exists are the unlock message and character select descriptions, Although it's possible that Metal Sonic uses the unused code for both of them.
- Menus pertaining to a global online network that collects completion times for stages and other data for player rankings can be found in the game but they aren't usable. The original game had a similar feature but it was never completed in Adventure 2, even though the menus and even audio relating to it were left in the files. The HD rereleases would implement their own online leaderboards, but in a much simpler format than what was planned.
- As they did with the first Adventure game, Resaurus planned to release a line of action figures to tie in with this game, which would have included Shadow, Rouge, Super Sonic, and Dr. Eggman. Unfortunately, due to Resaurus having gone out of business, this toyline was scrapped.
- If the demo and trial versions of the track are any indication, City Escape was originally intended to be an instrumental track in the vein of the other Sonic tracks at one point before it became a vocal track. A remixed instrumental version would eventually make it into the Downtown Race stage of the official release's multiplayer.
- Dummied Out character dialog for the President of the United Federation and his secretary suggested they were going to talk during the True Final Boss Battle and the finale, perhaps via Rouge patching them in over the radio.
