Animation of Tails performing an unknown move. A sprite of this was also seen in a pre-release screenshot.
Leftover animation of Amy performing her second hammer attack, originated from Advance 1.
Unused animations of Sonic and Knuckles from Advance 1, originally planned for when a stage’s gravity changes.
While it is unknown whether there were plans to incorporate the previous idea into Egg Utopia and XX Zone, Cream received new sprites based on these. Additionally, unlike Sonic and Knuckles, Tails and Amy received partial updates to their respective animations.
Animations of the entire playable cast fall-landing after using a spring. Just like in Advance 1, and even though they were updated, these ended up unused.
Follow-up falling animations of the entire playable cast after being hurt while running at full speed. This behavior is not seen in- game.
Transition frames of the entire playable cast in the Special Stage, just as they are about to finish skidding. In the game, the animation abruptly cuts to the standing frame.
Animations of the entire playable cast being hit by Robot Guard/Zero while moving from the side in the Special Stage. In-game, only the front-view version of these animations is played.
An early version of Cream's animation for the normal ending sequence, behaving the same as the rest of the playable cast. This was likely created before her mother, Vanilla, was added.
The rest of Cream’s last walking animation in the opening sequence of True Area 53 Zone, of which only the first of the eight frames was shown.
A partially unused frame of Tails in the opening sequence of True Area 53. Although it is present in the sequence, the big image of Super Sonic covers most of him.
Leftover sprites from Advance 1 of Sonic transforming into Super Sonic, including his sparks.
Unused turning frames for the Aero Egg boss.
Unused frames of a banging drum that could have been a spring, fitting in Music Plant.
White text for the title screen that says "TGS ver.". Used at the Tokyo Game Show event in 2002.
An unused background that can be seen in a trailer that was included in Sonic Mega Collection. It's the same background used in the options menu but in a different shade of blue.
This animation of Cheese rushing forward is used during the True Area 53 intro cutscene. Though the animation seems to be purely unique to that cutscene, it can be seen in some pre-release screenshots that it was originally an early version of Cheese's lock-on attack animation.
Each Zone has four Acts. The first two Acts are the regular Acts, while Act 3 is the Zone's "Boss Attack" Act - Act 4 goes unused for all Zones. All instances of Act 4 use the same foreground (a single platform with a roof of spikes, based on the Super Eggrobo Z's arena at the end of XX), as well as the background from the corresponding Zones.
Sonic Advance had the option to enable team play when playing in multiplayer modes. Such a feature was dropped for Sonic Advance 2, however coding for team play remains in the game. It can be enabled via hacking the game to call the team play setup screen after multiplayer connection has been initialised.
Team play is largely complete, and teammates can interact with each other. Code for team-specific character actions is left over from Sonic Advance, though is partially functional:
Sonic's team action (boosting teammates with his Spin Dash) works as intended.
Tails' and Knuckles' team actions (carrying teammates while flying/gliding) will cause their teammate to be stuck in the air with no way to control them.
Amy's team action (catapulting teammates upward with her Piko Piko Hammer) doesn't function at all.
Cream has no team action coded for her.
Graphical glitches will also occur on the results screen for players from the winning team, but not for losing players.
This needs some investigation. Discuss ideas and findings on the talk page. Specifically: Verify that this is intentional behaviour and not just a bug.
Not having an SRAM chip on the cartridge will unlock everything in the game. This is also the case for the other Sonic Advance games.
A grammatical error is present in the title card of True Area 53 in the Japanese version. This was corrected is the North American version but is oddly still present in the European version.
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