This game has a prototype article
Sonic Rush is Sonic's DS debut, which also introduced Blaze the Cat.
See if the Sonic Advance 3 leftover voice clips from the E3 demo are still present. Try the downloadable demo (in the options menu) out for any oddities. There are more unused graphics (ac_sonic.bac, ). A map oddity.
Found with the other graphics, and helpfully prefixed with "e3" are these images. They can be seen in the E3 demo. e3_comsoon_jpn.bbg is a bit more descriptive than the _eng version, and says "Thank you for playing. Play the retail version to see what comes next!".
z82   . Try accessing the level in game via file swapping, to determine what music, background, timer and collision it uses.
A 4 frame animation of a seal animal buddy like the ones that pop when you destroy an enemy, it's different than the one used in-game.
A complete animated spriteset for Sonic Advance 3's Akatento and Aotento badniks, seems to be a leftover from that game. The transparency is also broken. It should be noted that it's found alongside the final game's enemies.
Every boss map has a normally unseen 2D level that is used for collision and items for the boss battle. The example to the left shows the Level z13 (Zone 1 Act 3). Trying to load these levels as a non boss fight level will have various glitchy effects.
Unused Music Portions
After the Fight
Kick the Eggman
The two Boss Defeated themes normally cut off after around 7 to 12 seconds, but are actually about a minute and 30 seconds each. They can be played at full length in the Sound Test, known as "AFTER THE FIGHT" and "KICK THE EGGMAN" when the game is in English, but they do not feature in the official soundtrack.