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Sonic the Hedgehog 2 (Genesis)

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Title Screen

Sonic the Hedgehog 2

Developers: Sonic Team, Sega Technical Institute
Publishers: Sega (JP/US/EU), Tec Toy (BR)
Platform: Genesis
Released in JP: November 21, 1992
Released in US: November 24, 1992
Released in EU: November 24, 1992
Released in BR: 1994


AreasIcon.png This game has unused areas.
GraphicsIcon.png This game has unused graphics.
MusicIcon.png This game has unused music.
SoundIcon.png This game has unused sounds.
DebugIcon.png This game has debugging material.
LevelSelectIcon.png This game has a hidden level select.
Carts.png This game has revisional differences.


ProtoIcon.png This game has a prototype article
PrereleaseIcon.png This game has a prerelease article

Featured article

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.

Debug Functions

Level Select

Sonic The Hedgehog 2 Genesis Level Select.png

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.

Debug Mode

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 FFFFFA:0001.

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.
  • While the game is paused, some debugging options are 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. You must also be playing as Sonic, as Tails cannot enter object placement mode.

"Night Vision" Mode

Sonic2 Black Layers.png

Go to the Level Select screen, enable Debug Mode, then hold C and press Start when selecting a level. This will cause the console's VDP to activate a debug function: background graphics drawn behind the sprite layer will be covered with a translucent black overlay.

Moving Background Debug

Use PAR code 00EBEC:4E71 (Rev. 00), 00EBC0:4E71 (Rev. 01), or 00EBC2:4E71 (Rev. 02) to enable a special debugging feature: Hold 2P Up or 2P Down to move the rising floor / lava in Hill Top and the moving clouds in the background of Wing Fortress.


(Source: Sonic 2 Disassembly)

Cheats

  • All 7 Emeralds: To get all 7 Chaos Emeralds, unlock the Level Select screen and play sounds 04, 01, 02, 06.
  • Extra Continues: For 14 extra continues, play sounds 01, 01, 02, 04 on the Options screen. This cheat makes Oil Ocean Zone music play all the time due to an incorrect sound command.

Unused Graphics

Sonic

Graphic Frame ID Description
S2-Sonic falling.gif
52-53 An animation very similar to one used in Wing Fortress Zone when Sonic grabs the panels on the side of the ship. However, this is vertical.
Sonic2SonicAltDeath.png 5E An alternate death frame, defined in animation 16. This returns from (and is also unused in) Sonic 1.

Robotnik

Graphic Name Description
Spr cpzboss.gif
Unused CPZ Animation There's an unused animation for Robotnik accidentally dropping the blue goop on his own head in the Chemical Plant Zone fight. This animation has been around since the Nick Arcade prototype, but it was never implemented. There's a fix to implement the lost animation here.
Sonic2-RobotnikLaugh.gif
Robotnik laugh In Death Egg Zone, Robotnik is programmed to laugh when Sonic takes damage during the Silver Sonic battle. However, as there are no Rings in this Zone, Sonic instead dies immediately when hit and all animation is frozen, so this is never normally seen. In the 2013 mobile remake, this animation is not frozen when the player dies. You can also view the animation in the Sonic Jam port by playing in Easy mode, as well as the 3DS port by playing in Ring Keeper mode.

Other

Graphic Name Description
HPZiconS2.png
HPZ Icon A Level Select icon for Hidden Palace Zone. It is not normally used in any version of the game, but Pro Action Replay code 0096D8:0303 will cause it to replace the Emerald Hill icon in the Stage Select. It also appears in Sonic the Hedgehog 3's level select, which contains icons for the Sonic 2 Zones.
Sonic2CPZSirenLight.gif
CPZ Decorative object Unused decorative objects for Chemical Plant Zone, stored at 0x0383-0x0393 in VRAM. These can be placed in the iOS/Android 2013 version's debug mode.
Sonic2OOZSpringHolder.png
OOZ spring holder A holder for the OOZ ball launcher (see below). This appeared in the Simon Wai prototype, and is still loaded into VRAM in the final game.
Sonic2AquisAngry.gif
Sonic2AquisSpray.png
Unused Aquis graphics An unused animation for Aquis spitting up oil, along with an oil spray.
Sonic2gen Balkiry2.png
Unused Balkiry frame An unused frame of the Balkiry badnik from Sky Chase Zone with its landing gear deployed. 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.
S2-Turtle.gif
Walking turtle 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. This would later on make an appearance in Sonic Mania, shortly before the Metal Sonic boss battle at Stardust Speedway Zone.
S2-Picky.gif
Picky 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.
(Source: Sonic Retro)

Unused Objects

CPZ Hovering Platform

Sonic2CPZFloatPlat.png
Object ID: 0C

This object has been around since the Nick Arcade prototype. Every 1024 frames, it will slowly rise up for 128 frames, float in the air, then come back down 128 frames later. The amount of time it floats in the air is 128*(lower four bits of subtype) frames. The upper four bits can be used to offset when it starts to rise in the air.

HPZ Blocker

Sonic2HPZBlocker.png
Object ID: 12

This crystal was used in the earliest two prototype to block off a tube in Hidden Palace Zone. The graphics are long gone, but the code is still there, such as it is. It's a simple solid indestructible object and its coding hasn't changed since the Nick Arcade prototype.

HPZ Waterfall

Sonic2HPZWaterfall.gif
Object ID: 13

Another Hidden Palace Zone leftover. Again, the graphics no longer exist in the ROM. Its height is equal to 16*(lower five bits of subtype)+16 pixels. Placing one with a subtype greater than 17 will spawn garbage objects on the right.

Green Hill Zone Spinning Spiked

Object ID: 17

A leftover from Sonic 1. Unfortunately, the graphics have been deleted, but the coding is intact.

OOZ Ball Launcher

Sonic2-SpringBall.gif Sonic2OOZCheckeredBall.gif
Object ID: 46

A ball and spring object, which can be placed in Oil Ocean Zone via debug mode. If a switch is placed near it and pressed, the ball will pop out and start rolling in whichever direction Sonic was facing when the object was placed. It seems this object would have been used to cross something, as it can be stood upon, much like the ball object that appeared in early versions of Sonic the Hedgehog. It does not collide with breakable floors or elevators, and it will go up slopes and even vertical walls without slowing or stopping. It can be seen in the Simon Wai prototype.

MZ Small Platform

Object ID: 6C Although very similar to the small platforms used in Metropolis Zone, this platform behaves strangely, usually rising at an angle.

MCZ Ring Platform

Sonic2-mrzobject.png
Object ID: 73

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.

WFZ Turbine Fire

Sonic2-giantlaser.gif
Object ID: B7

If the sub-ID of the rotating platforms in Wing Fortress Zone has bit 02 of their subtype set but not 04, some kind of laser will appear (with no sound effects) when the platform spins. This object can be placed with debug mode, where it oddly appears before the used platform in the object list.

WFZ Pole Badnik

Sonic2-wfz-spinnything2.gif
Object ID: BF

A strange object that seems to be a spinning pole, which can be placed in Wing Fortress Zone via debug mode. It's like a badnik: you can destroy it, and it can damage you, but it doesn't move.

Unused Subtypes

Monitors
Sonic2MonitorStatic.gif
If the subtype of a monitor is set to 00, the monitor will spawn with a static icon. Breaking the monitor will harm the player.

CPZ Tipping Platform
The amount of time that the platforms in CPZ can stay flipped is variable -- equal to 10+(upper four bits of the subtype) -- but in the final game, the upper four bits are always set to 70.

ARZ Door
Sonic2gen Aquatic ruin door.png
An unused door from Aquatic Ruin Zone, which like similar doors in other Zones closes as soon as the player enters it. These can be placed via debug mode.

CPZ Bubble Snakes

Sonic2 CPZBubbleSnake.png

The blue bubble snakes in Chemical Plant Zone have many subtypes that define their movement pattern (00-0F for jumping back and forth, 10-1F for jumping between the floor and ceiling) and their length, which can be any number of segments between 1 and 16. However, only those that are 6 segments long are used (subtypes 05 and 15), leaving all other subtypes unused.

OOZ Pressure Stopper
Sonic2OilOceanPressureStopperH.png
The used pressure stopper in Oil Ocean Zone launches the player upwards. If the object subtype is set to zero, as it is in edit mode, it will launch the player to the right. This would have been used in the Simon Wai layout of the stage, but has no purpose in the final layout.

Unused Score Tally

Sonic2UnusedScoreTally.png

This configuration for the score tally, replacing "ACT #" with "ZONE", is meant to be used in levels with only one act, such as Sky Chase Zone, Wing Fortress Zone, and Death Egg Zone. However, none of those levels have a score tally, so this text never appears unless a capsule is placed via debug mode and destroyed. This was later used in Hidden Palace Zone in the 2013 remake.

Unused Audio

Music

The song at entry #10 in the Sound Test is unused in normal gameplay; however, it will play if 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.

(Source: Sonic Retro)

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 the Hedgehog 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 the Hedgehog and other unused sounds can be heard in the Sound Test.

Sound ID Sound Description
Sonic the Hedgehog Leftovers
$29
The sound used when hitting the R, UP, and DOWN blocks in the Special Stage.
$31
Electricity sound from Scrap Brain Zone.
$3A
The sound made while hitting the colored diamonds in the Special Stage.
$43
The warp noise made by a Giant Ring at the end of an act if Sonic enters it. This sound was later reused in Sonic the Hedgehog 3.
$47
Chain pulling sound from Marble Zone.
$49
Bonus point tag appearing at the end of an act.
Other Unused Sounds
$38
Sounds similar to the sound of spikes popping up. This is also unused in Sonic 1.
$51
Unknown. Sounds like something popping or skidding on the ground.
$52
A low siren, similar to $53 which is used in the 2-Player mode.
$68
Appears to be a slightly shorter version of Mystic Cave Zone's bridges stopping in place ($69).

Inaccessible Rings

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

Image Level Approximate coordinates Description
Sprites Always on Top enabled in Gens. Aquatic Ruin Zone
Act 2
1FA90626
Sprites Always on Top enabled in Gens.
Two rings lined up horizontally. The rightmost can actually be touched without going inside the pillar, but there's no way to reach it.

The pillars weren't there in Beta 4, allowing the rings to be collected.

Sonic 2 CNZ2 rings.png Casino Night Zone
Act 2
027F00F8 Two clusters with seven rings each, just above the start, but way too high to reach.

When locked-on to Sonic & Knuckles, it is possible for Knuckles to collect these rings by gliding to the far left from the highest wall.

Sonic 2 CNZ2 rings2.png Casino Night Zone
Act 2
10700611 No known layout between the Simon Wai and "Beta 4" prototypes resembles this line of rings, and the level design may have changed between these two prototypes. The set of rings could be picked up using the lift.
Sonic 2 MCZ2 hidden rings 1.png Mystic Cave Zone
Act 2
0F2B00F0
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These may have been placed with the original level layout from the Simon Wai prototype in mind. In the same coordinates in that prototype is a tall pillar.
Sonic 2 MCZ2 hidden rings 3.png Mystic Cave Zone
Act 2
15880160
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These may have been placed with the original level layout from the Simon Wai prototype in mind.
Sonic 2 MCZ2 hidden rings 2.png Mystic Cave Zone
Act 2
16050156
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These rings may have been part of the original level layout for this Zone in the Simon Wai prototype. As there is a ledge and an empty space in the same coordinates in that prototype, a swinging platform may have been in these coordinates to accompany the rings.
Sonic 2 OOZ hidden rings.png Oil Ocean Zone
Act 2
0BC003A8
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These are leftovers from the original level layout seen in the Simon Wai prototype. The same rings can be found in the same coordinates in that prototype.
Sonic 2 OOZ hidden rings2.png Oil Ocean Zone
Act 2
11BF023A
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These are leftovers from the original level layout seen in the Simon Wai prototype. The same rings can be found in the same coordinates in that prototype.
Sonic 2 OOZ hidden rings3.png Oil Ocean Zone
Act 2
12C0023A
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These are leftovers from the original level layout seen in the Simon Wai prototype. The same rings can be found in the same coordinates in that prototype.
Sonic 2 OOZ hidden rings5.png Oil Ocean Zone
Act 2
191001F8
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These are leftovers from the original level layout seen in the Simon Wai prototype. The same rings can be found in the same coordinates in that prototype.
Sonic 2 OOZ hidden rings4.png Oil Ocean Zone
Act 2
1A0001F8
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These are leftovers from the original level layout seen in the Simon Wai prototype. The same rings can be found in the same coordinates in that prototype.
Sonic 2 OOZ hidden rings6.png Oil Ocean Zone
Act 2
20880300
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These are leftovers from the original level layout seen in the Simon Wai prototype. The same rings can be found in the same coordinates in that prototype.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 2
02C0043F
Rings placed via Debug Mode to show how they would have looked in the prototype layout.
Three horizontal slanted rings, under the floor with the ten-ring box and a cog nearby. This floor used to be a slope in the Simon Wai prototype, so these rings may have been placed with the slope in mind.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 2
135000D0
The level design was copied from Simon Wai to the final version of Sonic 2 so that the objects were placed correctly.
These rings may have corresponded with the original level layout from the Simon Wai prototype. Judging by the layout in that prototype, these rings could have been reached by jumping from the nearby conveyor belt.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 2
0F000169
Rings placed via Debug Mode to show how they would have looked in the prototype layout.
These rings appear to correspond with the original level layout from the Simon Wai prototype. There is a ledge in the same coordinates in that prototype, so the rings may have been placed on top of it.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 2
0F400354
Rings placed via Debug Mode to show how they would have looked in the prototype layout.
These rings appear to correspond with the original level layout from the Simon Wai prototype. In the same coordinates, they would have been under a ceiling.

Misplaced Objects

Various objects throughout the levels are misplaced or in odd positions, possibly indicative of earlier level designs.

Image Level Approximate coordinates Description
Sprites highlighted enabled in Gens. Aquatic Ruin Zone
Act 2
08E606CC A misplaced air bubble object.
Sprites Always on Top enabled in Gens. Hill Top Zone
Act 1
128A020C This poor seesaw was overlooked once the layout was altered from the Simon Wai prototype.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 3
0A89026C This object, found next to an invincibility monitor, acts like spikes despite not using spike graphics. It serves the practical purpose of preventing zipping bugs.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 3
116905AC A door object with no use or any real reason to exist.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 3
1D1F054D A platform that moves if Sonic is underneath it. This seems to fit with the Simon Wai prototype's layout.
Sprites Always on Top enabled in Gens. Metropolis Zone
Act 3
1F75056C Either a lava pit was intended to be here, or this is another anti-glitch trick.

Scrapped Zone Remains

Unused Zone #1 (ID 01)

Empty, with only a Tails life icon.

This is an empty level slot that exists in the game, which was possibly used by Labyrinth Zone in the Nick Arcade prototype. It can be accessed via Pro Action Replay code FFFE10:0100 or Game Genie code ACLA-ACD8 (AB6X-ACBR when locked-on to Sonic & Knuckles), and choosing "Sound Test" on the stage select menu (Special Stage with lock-on). This stage is an objectless version of Emerald Hill Act 1. Additionally, it has a Tails icon, much like the Wood Zone remains. Finishing Act 1 by hacking in an animal capsule will send you to Emerald Hill Zone Act 1.

Wood Zone (ID 02)

The original color palette is all that's left.

The level slot containing Wood Zone in the prototypes 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 FFFE10:0200 or Game Genie code ACLA-AECY (AB6X-AEBR with Sonic & Knuckles lock-on) and selecting Emerald Hill Act 1 (or by simply starting the game with the code active) or selecting Special Stage in Knuckles in Sonic the Hedgehog 2) in the level select leads to an objectless (since Wood Zone had no objects to begin with, even the debug object listing only has rings and teleport monitors) version of Emerald Hill Zone Act 1 with Wood Zone's palette, Metropolis Zone's music and some glitchy collision. For some reason, the Zone shows Tails's life counter with no number, and when locked on to Sonic & Knuckles the life counter's text is red. Some sprites from Metropolis Zone can be loaded into this zone. If you hack in an animal capsule and clear Act 2, you'll go to Metropolis Zone.

Unused Zone #2 (ID 03)

Only Oil Ocean Zone music is played.

Another empty stage can be accessed with Pro Action Replay code FFFE10:0300 or Game Genie code ACLA-AGD8 (AB6X-AGBR with Sonic & Knuckles lock-on), and like with ID 01 above, it can be accessed by choosing "Sound Test" on the stage select screen (Special Stage with lock-on). This stage is nearly identical to ID 01, with the only differences being that some of the background is still intact, as well as the fact that it uses Oil Ocean Zone's theme as its default music. Badnik sprites from Metropolis Zone and Emerald Hill Zone are loaded. This level slot belonged to Emerald Hill Zone in the Nick Arcade prototype and then went unused in the Simon Wai prototype. Finishing Act 1 will send you to Emerald Hill Zone Act 1. Presumably, this slot was meant for Dust Hill.

Hidden Palace Zone (ID 08)

Various objects and items remain the same as they were in the Simon Wai prototype. This level was untouched since.

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 16×16 mappings, the level layout points to Oil Ocean Zone Act 1, and the Badniks' code was removed. By using Pro Action Replay code FFFE80:0200 or Game Genie code ACLA-ATD4 (ACLA-ATDR in the "Rev. 00" version of the final, and AB6X-ATBR with Sonic & Knuckles lock-on) and selecting Death Egg in the level select (Special Stage in Knuckles in Sonic 2), 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 second Act can be accessed with the code AGLA-ATD4, and finishing it by placing an animal capsule with debug mode will take you to Oil Ocean Act 1.

Much like it was in the Simon Wai prototype, it is otherwise identical to how it was in the Nick Arcade prototype, with the only difference being a lack of badniks, garbled graphics, and almost nowhere to stand on. Decorative objects, platforms, bridges, water, rings, shield, and Tails 1-Up monitors can be found if you use debug mode to navigate the level.

Unused Zone #3 (ID 09)

Empty and strange.

Another empty level slot, which can be accessed by using Pro Action Replay code FFFE80:0900 or Game Genie code ACLA-AWD8 (AB6X-AWBR with Sonic & Knuckles lock-on) and choosing "Sound Test" (Special Stage with lock-on) in the level select. This version of the stage uses garbled Emerald Hill Zone tiles and badnik sprites from Oil Ocean Zone are loaded, has very little collision data, and no objects present within the debug menu, making it impossible to finish by any means. Unlike the Simon Wai prototype, the default background music is the same as Sky Chase Zone. When finished by hacking in an animal capsule, you'll go to Emerald Hill Act 1.

Removed Zone (ID 11)

Some of the pointers in Sonic 2 that control things such as zone specific pattern load cues, list another entry after zone 10. Whether or not this is simply an error is unknown, but it is worth noting that 18 zones were originally planned, and that this removed zone would bring the total zone number to 18. Trying to access this zone in the final simply crashes the game on the title card. It's likely this zone was never fully implemented before it was scrapped.

Unused Oil Ocean Zone Background Section

Oil Ocean Zone's background

Oil Ocean Zone's background layout is 768 pixels wide internally, but the game only uses the first 512 pixels. Sonic 2 has 64×32 tiles (512×256 pixels) loaded at a time, and loads new tiles on the edges as you move around the level. OOZ's scrolling code doesn't reload any tiles as you move horizontally, leaving you with the same horizontal area of the background that you started with. Presumably, this is because the tile loading would eventually overwrite the tiles used for the sun, which never moves.

Oddities

CPZ/DEZ Door

In-game sprite Correct sprite
Sonic2 IncorrectDoor.png Sonic2 CorrectDoor.png

The door sprite in Chemical Plant Zone and Death Egg Zone is actually assembled incorrectly. By using Debug Mode to place a door, you can see how the door's sprite is supposed to be assembled, using 8×8 tiles that go unused due to the incorrect sprite assembly. The reason for this is because the doors use the object subtype $00, the subtype meant to be used by the doors in Hill Top Zone, rather than subtype $02 which is meant to be used in Chemical Plant and Death Egg.

The 2013 rerelease uses the correct sprite for the doors.

Duplicate Rings

A column of rings found next to a giant cog at coordinates 08F005E8 if you take the path to the right after the first yellow spring shaft in Metropolis Zone Act 2 is very unusual. Each ring collected gives you four rings instead of one, for a total of 12 rings. This is because these rings are actually four columns of rings that are all laid out on top of each other in the same coordinates. This oddity is still there in the 2013 remake.

Unused Level Chunks

Emerald Hill Zone only:

Emerald Hill Zone or Hill Top Zone:

Hill Top Zone only:

Chemical Plant Zone:

Casino Night Zone:

Mystic Cave Zone:

Oil Ocean Zone:

Note that none of the unused chunks are in the table that the game checks to determine whether or not Sonic & Tails should slide.

Metropolis Zone:

Wing Fortress Zone:

Unused 2x2 Tiles

Tiles loaded in the VRAM are organized by spreadsheet in the RAM address FF9000, at this point IDs are created for each line representing 2x2 of the graphics of the VRAM. The address FF0000 is in charge of adding mirroring and collision to the tiles 2x2, creating a 8x8 chunk, and in all there are 256 chunks created from FF00000. To add these chunks, add the IDs below in this format 0xxx from FF0000 and search for the chunk ID 00 on the level. It is possible to see some unused graphics that are referenced below.

Zone Image IDs
Oil Ocean Zone

017, 01B, 081, 08D, 093, 0B2, 0B3, 0C8
0C9, 0D0, 0D1, 0DB, 0DC, 0F3, 0F4, 114
11C, 11D, 11E, 123, 124, 125, 126, 127
128, 129, 12A, 12B, 12C, 12D, 12E, 12F
130, 131, 134, 139, 13A, 13F, 141, 144
146, 147, 157, 15B, 182, 183, 184, 187
189, 18A, 18E, 1AB, 20F, 210, 216, 217
218, 250, 25E, 262, 263, 270, 272, 27E
28A, 28B, 293

This mapping includes several unused graphics and one of them more known was used in Simon Wai Prototype for the object spring and ball.

Metropolis Zone

023, 024, 025, 026, 028, 029, 048, 049
04A, 04B, 04C, 04D, 04E, 04F, 050, 051
052, 053, 054, 055, 056, 057, 058, 059
05A, 05B, 05C, 05D, 05E, 05F, 060, 061
062, 064, 065, 066, 067, 068, 09F, 0C2
134, 135, 136, 137, 138, 139, 13A, 13B
13C, 13D, 13E, 13F, 140, 141, 142, 143
144, 145, 147, 174, 17B, 196, 197, 198
199, 19A, 19B, 19C, 19D, 19E, 1A1, 1A2
1AF, 1B0, 1B1, 1B2, 1B3, 1B4, 1B5, 1B6
1B7, 1B8, 1B9, 1BA, 1BB, 1BC, 1BD, 1BE
1BF, 1C0, 1C1, 1C2, 1C3, 1C4, 1C5, 1E4
1E6, 1E7, 1E8

It is still possible to see leftovers from the Level Design of the areas used by the lozenge lift from the Simon Wai prototype, it is also possible to see silver-colored pipes never used, possibly used as background.

Sky Chase Zone/Wing Fortress Zone

147, 14D, 151, 157, 162, 16C, 1BB, 1F8
1FE, 1FF, 201, 210, 211, 215, 219, 21A
227, 228, 259, 262, 268, 27C, 2A0, 2A2
2B7, 2E3.

This zone didn't have many interesting things except that there is a kind of railing and various tiles with unused graphics and clouds from the Sky Chase Zone.

Early Wing Fortress Zone

Sonic2 Early Sky Fortress.png
A small piece of the Wing Fortress Zone appears in Sky Chase Zone, but you will not be able to see it completely.

The Wing Fortress has several differences from the final version. It is possible to note that some windows have been removed and others added, in addition to rivets, a long metal frame in the left and a small platform near the propellers of the lower left corner.

Revisional Differences

There are three revisions of Sonic the Hedgehog 2, known as Rev. 00, 01, and 02.

Region Switch Code: On the title screen, press Up, Down, Down, Down, Up, and a ring sound will be heard. This switches the game between Japanese and International mode. In Japanese mode, references to "Tails" are changed to Miles, and the trademark symbols are removed from the SEGA screen and title screen.

Rev. 00

The original release. The following errors are only present in Rev. 00:

Rev. 00 Rev. 01
Sonic2CasinoNightSignpostRev00.png Sonic2CasinoNightSignpostRev01.png
  • 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.

Sonic2Rings1000Rev00.png

  • Ring monitors ignore the 999 ring cap, leading to bugged graphics in the ring counter.
Rev. 00 Rev. 01
Sonic2KalinskeRev00.png Sonic2KalinskeRev01.png
  • The credits misspell Thomas Kalinske's name as "Tohmas Kalinske".
  • Wing Fortress Zone's checkpoints are bugged: activating one will cause the later ones to appear as if they're activated, too.

Sonic2TeleportBug.png

  • Sonic and Tails briefly display garbled art after activating a Teleport Monitor in 2-player mode. This seems to be the result of both players using the other players' tilemap but applied to their own graphics. Rev. 01 fixes this by making the players invisible until they start moving again.
  • The yellow spring walls in Metropolis Zone can be bounced on while hurt, which freezes the character's animation and locks the controls.
  • If the big Casino Night Zone springs are landed on while hurt, the character enters a glitched state: they don't enter their rolling state, and remain able to walk, but are still treated as if they're attached to the spring.

Rev. 01

The much more common, bugfixed version of the game. Changes in Rev. 01 include:

Rev. 00 Rev. 01
Sonic2CasinoNightFlippers2PRev00.png Sonic2CasinoNightFlippers2PRev01.png
  • Two flippers in the 2-player version of Casino Night Zone Act 1 changed positions. The Crawl placement in Act in the 2-player version of Casino Night Zone, Act 1 matches Beta 8's placement.
  • The flipper and Crawl placement in Act 2 of the 2-player Casino Night Zone matches Beta 8's placement.
Rev. 00 Rev. 01
Sonic2InvisibleBlocksRev00.png Sonic2InvisibleBlocksRev01.png
  • "Invisible wall" objects are no longer visible in debug mode.
Rev. 00 Rev. 01
Sonic2BumperObjectRev00.png Sonic2BumperObjectRev01.png
  • The objects that handle the collision for Metropolis Zone's yellow spring walls are no longer visible in debug mode.

Rev. 02

Released as part of Sonic Classics, this iteration fixes several more bugs, including:

  • A crash that would sometimes happen if Sonic defeated a Rexon in Hill Top Zone.
  • The player being able to spindash off the Tornado in Sky Chase Zone. (This error was reintroduced in the 2013 version.)

Sonic2SuperSonicEndBug.png

  • The ability to transform into Super Sonic at the end of a level, which would get the player stuck in the air (and prevent the level from being completed)

Sonic2WingFortressBug.png

  • The background speed and offset variables not being reset if the player continues from a checkpoint in Wing Fortress Zone. This is only a problem if the player gets a Time Over during the WFZ ending sequence.

Sonic2Rev02FlipBug.png Sonic2Rev02FlipBugGrabber.png
However, this revision introduces a bug where Grabber's legs and Silver Sonic's flame and sparks aren't properly flipped if they're facing right.