|ARZ Barrier||Unused door barriers from Aquatic Ruin Zone.|
|Unused Balkiry Frame||Unused frame of the Balkiry badnik with landing gear. It's possible that they were originally intended to take off from the Wing Fortress as it passed by. If a Balkiry is selected in debug mode, this sprite will be seen instead of its flying one.|
|Walking Turtle||Walking sprites of the turtles that pop out of the badniks in Sky Chase Zone. Normally you'll never see this, since the animal never has the opportunity to hit the ground.|
|HPZ Icon||Level Select icon for Hidden Palace Zone, which never made it into the final game. The art however, is present in Sonic 3's level select. Pro Action Replay code 0096D8:0303 will cause it to replace the Emerald Hill icon in the Stage Select.|
|WFZ Laser||Large laser shooting through a spinning platform in Wing Fortress Zone. Never seen in-game.|
|MCZ Ring Platform||Weird platform made of rings, placeable using debug mode. It moves back and forth depending on which side you stand on.|
|WFZ Spinning Pole||Weird spinning pole that acts like a badnik - you can destroy it, and it can hurt you, but it doesn't actually move.|
|Static or blank TV Monitor||Powerup monitor which harms you when broken. Never seen in-game.|
|Unused Animal||Picky, a returning animal from Sonic 1, is present in Death Egg Zone. However, there are no badniks or animal capsules, so he's never seen.|
|Robotnik Laugh||In Death Egg Zone, getting hit with one or more Rings during the Silver Sonic battle causes Robotnik to laugh. However, this is never actually seen outside of debug mode because the Zone has no Rings. In the 2013 mobile remake, this animation can be seen normally if the player dies during the fight. In 3D Sonic the Hedgehog 2 it can also be seen if the player is hurt by Silver Sonic if the Ring Keeper mode is on.|
This configuration of the score tally is unused but was meant for levels with a single act (Sky Chase Zone, etc). It can be made to appear by using debug mode and placing, then breaking a capsule.
In the sound test, song $10 is actually a unused song. This has been established to be the music meant for Hidden Palace Zone.
There are a few sound effects leftover from Sonic 1 and can be heard in the sound test.
Sounds not used anywhere in the game can be heard in the sound test.
The level order that is used during gameplay is actually quite different from the intended order according to the level slots. A simple level select Pro Action Replay code (FFFE10:??00) can be used to verify this:
|Order in gameplay||Actual|
|Emerald Hill Zone||Emerald Hill Zone (00)|
|Chemical Plant Zone||Metropolis Zone (04/05)|
|Aquatic Ruin Zone||Wing Fortress Zone (06)|
|Casino Night Zone||Hill Top Zone (07)|
|Hill Top Zone||Oil Ocean Zone (0A)|
|Mystic Cave Zone||Mystic Cave Zone (0B)|
|Oil Ocean Zone||Casino Night Zone (0C)|
|Metropolis Zone||Chemical Plant Zone (0D)|
|Sky Chase Zone||Death Egg Zone (0E)|
|Wing Fortress Zone||Aquatic Ruin Zone (0F)|
|Death Egg Zone||Sky Chase Zone (10)|
Level slots 01,02,03,05,09 all lead to Emerald Hill Zone and 08 is actually Hidden Palace. In the Simon Wai prototype some of these were used for scrapped levels. 02 was used for Wood Zone and 0E was used for Genocide City Zone.
Commentary found in the Sonic Jam strategy guide reveals that the level order could have been even more different. It states that Chemical Plant Zone was meant to be the 10th zone back when the game was planned as an 18 zone game.
There are some levels that have rings in places that can't be reached normally. This makes getting a Perfect bonus in these stages impossible.
|Aquatic Ruin Zone
|1FA90626||Two horizontally lined rings.|
|Casino Night Zone
|027F00F8||Two groups of seven rings. These are right at the start of the level but cannot be reached with a jump or using nearby objects.|
|Mystic Cave Zone
|16050156 + 1712016D||Three horizontally lined rings, and a nearby curve of rings, similar to ones found near swings. Both sets of rings are found in the ceiling.|
|Oil Ocean Zone
|1A0001F8 + 0B9F03B0 + 1245021C||Three horizontally lined rings, close to the launcher and invincibility monitor. Three vertically lined rings stuck in a block which prohibits access to them. Rings in a upside down v shape pattern. They are stuck inside the wall, thus unaccessable.|
|02C0043F||Three slanted rings, in the floor that has a ten-ring monitor and a cog close-by.|
|Sonic the Hedgehog 2 (16-bit)|