Sonic the Hedgehog 2 (Genesis)

Sonic the Hedgehog 2 is the sequel to the first game, which introduces Tails, the Spin Dash, and the idea of robot Sonics. A large number of interesting things were cut from the final version, such as the ever-famous Hidden Palace Zone.

Level Select/Debug Mode
Like the first game, Sonic 2 has a well-known level select:


 * Go into the Options menu.
 * In the sound test, play sounds 19, 65, 09, 17 (September 17, 1965 being Yuji Naka's birthday). This enables the Level Select.
 * Press start to return to the title screen. When the menu appears, hold A and press Start to bring up the Level Select screen.



Enabling the game's debug mode requires the level select to be enabled.
 * In the level select's sound test, play sounds 01, 09, 09, 02, 01, 01, 02, 04 (November 24, 1992 being the date of the game's US release).
 * Choose any level, then hold A and press Start. Keep A held down until after the title card pops up.

Alternatively, it can be accessed with Pro Action Replay code. From here, you have access to a variety of things:
 * Invincibility
 * Unlimited time
 * Debug Coordinates (in place of score)
 * Sprite Counter (in place of time)
 * Placement Mode: Press B to enter placement mode. From there...
 * Press A to move forward one object.
 * Hold A and press C to move backward one object.
 * Press C to place the object.
 * If the game is paused, some debugging options become available.
 * Press A to go back to the title screen.
 * Press and hold B to slow down the game by 50%.
 * Press C to advance the game by one frame.

In addition, if Sonic dies, he can be revived by entering Placement mode, moving to a safe spot, and exiting. Trying to place an object in this death state will freeze the game, however.

Unused Sprites


An unused door from Aquatic Ruin Zone, which closes as soon as the player enters it.



An unused frame of the Balkiry badnik from Sky Chase Zone standing on something. 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.



A walking animation for the turtles in Sky Chase Zone. The only way to see this sprite is by using debug mode to create and destroy a badnik while the Wing Fortress passes by.



A level Select icon for Hidden Palace Zone. It is not used in any version of Sonic 2, but does appear in Sonic the Hedgehog 3 's level select, which contains icons for the Sonic 2 levels.



A large laser shooting through a spinning platform, intended for Wing Fortress Zone.



An odd platform made of rings, which can be placed in Mystic Cave Zone via debug mode. It can be stood on, and moves in a similar motion to the spinning spiked balls in the level.



A strange object that seems to be a spinning pole. It's like a badnik - you can destroy it, and it can damage you, but it doesn't move. It might have appeared in Wing Fortress Zone, as it is placeable in debug mode there.



A monitor displaying static that harms you when broken. This monitor was also found in Sonic 1, although it didn't do anything when broken.

Music
The song at entry in the Sound Test is unused in normal gameplay, however, it will play when the corrupted remains of Hidden Palace are accessed in the final build through the use of cheating devices or otherwise hacking the game. It does not exist in the Simon Wai prototype, where instead the functional version of Hidden Palace uses the music that was later used for the 2-player version of Mystic Cave.

Disc 2, Track 37 of the Sonic the Hedgehog 1&2 Soundtrack contains Masato Nakamura's original demo version of this song, but it doesn't loop and then fade out like the Zone demo tracks; instead, towards the end of the track, the tune changes significantly and has a proper ending. This may suggest that the music was originally intended for some sort of cutscene, perhaps taking place in Hidden Palace. Interestingly, this track is referred to as "STH2 Unused Song ~ Masa's Demo version ~", without specifying its intended use, though all track titles can be taken to be indicative only of how each song was used in the final release version.

Although popular speculation is that this song was at one point intended to be used as the background theme for Hidden Palace, the 2013 port of Sonic 2 instead uses the same music as the Simon Wai prototype, as the developers felt that it better suited the revised level.

Sounds
A few unused leftovers from Sonic 1 can be heard in the Sound Test.
 * - The sound used when hitting the R, UP, and DOWN blocks in the Special Stage
 * - Electricity sound from Scrap Brain Zone
 * - The sound made while hitting the colored diamonds in the Special Stage
 * - The warp noise made by a Giant Ring at the end of an act if Sonic enters it
 * - Bonus point tag appearing at the end of an act

Inaccessible Rings
Some levels have rings in places that cannot be reached, making a Perfect bonus impossible.

Scrapped Zone Remains
The level slot containing Hidden Palace Zone in the prototypes actually retains the level's object layout and palette, but the art and block mappings point to Oil Ocean's 16&times;16 mappings, the level layout points to Oil Ocean 1, and the Badniks' code was removed. By using Game Genie code ( in the "Rev. 00" version of the final) and selecting Death Egg in the level select, you can see this for yourself. This level uses track 10 of the sound test (otherwise unused) and Oil Ocean's debug item list.

The level slot containing Wood Zone in the prototypes also has something left in the final, albeit less than Hidden Palace: palette, object layout, and music selection data. Accessing it via Pro Action Replay code or Game Genie code  and selecting Death Egg in the level select leads to an objectless (since Wood Zone had no objects to begin with) Act 1 of Emerald Hill, with Wood Zone's palette and some glitchy collision. The debug item list only has rings and teleport monitors.

Revisional Differences
There are two revisions of Sonic 2, known as Rev. 00 and Rev. 01. Rev. 01 is the much more common, bugfixed version of Sonic 2. The following errors are only present in Rev. 00:


 * The signpost in Casino Night Zone is a little too deep into the ground, resulting in the bottom portion of the goalpost being visible through the floor.
 * The ring counter can be corrupted by collecting 999 rings and opening a Super Ring Monitor, with nothing preventing an overflow.
 * The credits misspell Thomas Kalinske's name as "Tohmas Kalinske".

In addition, another version of Sonic 2, called Rev. 02, was released on Sonic Classics. It fixes a nasty bug that can crash the game if Sonic hits a Rexon in Hill Top Zone, but then adds some wrong sprite mappings to the Mecha Sonic object, causing the flame and sparks to come out the front of it instead of the back.