Sonic the Hedgehog (16-bit)/Hidden content

Level select

On the title screen, press . A ring sound will play - holding + will bring up the menu, which also includes a sound test.

If running the Japanese game on a Japanese system, the code is , then +.

This screen suggests the intended level order was different to what is seen in the final game, with every zone save for Green Hill Zone and Scrap Brain Zone (and Final Zone) changing positions. This order is reflected internally, as shown in the Action Replay codes at the bottom of this page.

Commentary found in the Sonic Jam strategy guide also confirms that Labyrinth Zone was originally intended to be the second zone but was moved due to its difficulty relative to Green Hill Zone.

Debug Mode

On the title screen, press . A ring sound will play - holding + until the title card appears will activate debug mode. Sonic will also be invincible.

If running the Japanese game on a Japanese system, the code is , then +.

Due to a quirk in Sonic 1, other sources will give variations of this code. The game looks for two (or four) presses during the sequence, but is not concerned about where they are placed - this means, for example, the hint in Sonic Jam, which specifies edit mode as , + is equally valid.

It is possible to activate both edit mode and the level select by separating the two codes (before +) with an button press. Alternatively, activating debug mode, pausing during gameplay and pressing will return to the title screen with the feature still activated. Holding during paused gameplay will activate slow-motion, and pressing will display the next frame (it can be pressed more times to show other frames).

Note that in the case of running the Japanese game on a Japanese system, these "pause options" will require an other code which is (it can be used in addition to "Debug Mode" and "Level Select" like other versions).

Hidden Japanese credits

On the Sonic Team Presents screen, text showing the full names of key staff members and their roles in development is placed behind the Sonic Team Presents text. You cannot see this, however, because both the text and the background color are black.

With a cheat code, however, the game will hide the Sonic Team Presents text and change the background color to white, showing the hidden credits. With the region set to Japan, press , , , , , , , , , , , for the Japanese version, or , , , , , , , , , on the International release; you should hear a sound confirming this. Then, when the demo starts, hold + + + and either press or wait for the demo to end. The Credits translated:

Program	Naka Yuuji
Plan	Yasuhara Hirokazu
Design	Ooshima Naoto Ishiwatari Jina Kataoka Rieko
Sound Produce	Nakamura Masato
Sound Program	Kubota Hiroshi Makino Yukifumi

Staff roll and ending sequence from level select (Japanese version on Japanese hardware)

+

Alternatively:

• , wait until the demo starts, press to stop the demo, enter Zone Select cheat.
• In the Sound Select, select 9E and press // to go to the Staff Roll, or select 9F and press // to go to the Ending Sequence (which will lead to the Staff Roll).

Staff roll and ending sequence from level select (International version on Japanese hardware)

+

Alternatively:

• , wait until the demo starts, press to stop the demo, enter Zone Select cheat.
• In the Sound Select, select 9E and press // to go to the Staff Roll, or select 9F and press // to go to the Ending Sequence (which will lead to the Staff Roll).

Misplaced objects

Crabmeat

There are multiple misplaced objects throughout the game. The above picture shows a misplaced Crabmeat in Green Hill Zone. It can be found at coordinates 10D0 0370.

Wall monitor

In Scrap Brain Zone act 2, a static monitor can be found inside a wall (above and to the right of a Super Ring monitor). It can be broken during normal play, but it does nothing. The graphics are largely obscured by the wall, but you can just about see the explosion and a corrupted tile when it is broken.

Missing shoe stripes

A couple of animations are missing the white stripes from Sonic's shoes. This could suggest stripes were added after much of the artwork was ready.

Unused content

Art

Sonic

Art	Description
	This sprite shows Sonic standing while gasping for air. This was presumably used in Labyrinth Zone.
	This animation shows Sonic holding his breath while running. It is speculated that this was used during the countdown to signify that Sonic must find air as soon as possible.
	This unused sliding sprite is similar to the one used in Sonic CD's Wacky Workbench Zone.
	As seen in a couple of prototype screenshots in magazines and in video footage from Sega Shinsaku Soft Video Vol. 7, Sonic would do a victory pose when jumping after passing a signpost. This was removed before the final version, possibly because its use was complicated by the addition of post-singpost Giant Rings, which cause Sonic to disappear.
	These Spin Dash–esque sprites are present in the final ROM, but their use is unknown. Some theories are that they were used for a move similar to the Spin Dash or that they are animations for some sort of warp movement, perhaps through winding tunnels. It’s also possible that a teleporter like the one found in the 8-bit version of Scrap Brain Zone would have played the animation.
	This set of sprites showing Sonic falling or shrinking are not used in the game, and their intended purpose is unknown. They might have been designed to simulate falling in the death animation, or for a speed tunnel that would extend into the background.
	A greyscale version of Sonic's death animation. His left foot is placed slightly differently.

Levels

Art	Description
	The two faces pictured here are not in their original palette, but they appear to be earlier versions of the faces on the totem poles of Green Hill Zone.
	These unused tiles were found in Green Hill Zone's tileset and appear similar to the areas used in the underground areas of Sonic the Hedgehog (8-bit)'s Green Hill Zone. These may have also been used for a cut underground area.
	This unused graphic can be found in the tileset for Spring Yard Zone. It is unused in the final game, and can be found in several prototype screenshots shown in magazine previews. The sign itself says "Let’s Go."
	An unused frame of the switch sprite. When bit 5 of a switch's subtype is set, it makes the object flash, using this sprite. In Labyrinth Zone, this sprite's data is partially overwritten by the cork sprite in VRAM. Marble Zone's switch has no equivalent sprite.
	This is a horizontal sprite of the Burrobot. Perhaps the Borrobot dug back into the ground after a certain amount of time?
	These lights were found in Star Light Zone's data but are not used.
	The three machines shown were found in Star Light Zone's dataset but are not used in the final game. They appear to have been background objects rather than obstacles.
	The left image shows the back of Robotnik's legs, which can’t be seen normally. The right image is what is normally seen.
	Bumper that appears to be a rosebud with an incorrect palette. The ending level shares its debug item list with the Special Stage, so the bumper is usable in both.
	Unused section of grass which does not seem to match with any palette in the game.
	Splats, a prototype Badnik that was cut late in the game's development. Splats is unique in that it went on to be featured in merchandise and comic books, but only the art remains in the final game.
	Some yellow goggles, possibly intended for Labyrinth Zone. Each frame of the graphic fits together with one of Sonic's poses.
	Unused graphics of Eggman exploding, possibly as part of an alternative ending sequence.

Special Stage

Note: All of these items can be seen in-game by using edit mode to fall outside the playing area of the special stage. It is easier to see them when advancing frame-by-frame by pausing and pressing .

Art	Description
	Although these icons are found in the object list for the special stages and their graphics exist in the ROM, they are unused in the final game and have no known function; when placed, they act like normal solid blocks. They are labeled Zones 1–6, suggesting that they may have warped Sonic to another Zone from within the special stage as a sort of shortcut, or they were likely to indicate which Special Stage the player was in or which stage they came from after reaching the signpost.
	Extra life icon for the special stages. It is listed in the North American and European manuals for the gameMedia:Sonic1 MD US SonicJam manual.pdfMedia:Sonic1 MD EU manual.pdf, but it never actually appears in any of the special stages. It is, however, fully functional, and can be placed in any special stage; when touched, Sonic gains an extra life and the icon disappears like a ring.
	An icon with the letter W on it. Its use is unknown, and it has no function when placed in-game. This block is solid. The Japanese often assocate the letter "W" with "double" which may give clues about its use.

Objects

Art	Description
	Eggman monitor that does nothing. Is likely intended to hurt the player, as it does in Sonic the Hedgehog 2 (16-bit)'s 2-player mode. To add a functional Eggman monitor in the game see the SCHG page on how to add it.
	Goggle monitor nothing. Had it been used, it would most likely have been accompanied by the unused goggle graphics and may have provided the ability to breathe underwater. To add a monitor which adds a goggle Monitor that uses the goggle sprites, use this SCHG page.
	Static monitor that does nothing. This is found in various areas of Scrap Brain Zone that the player can not normally access, such as inside walls. It is possible to break one of them, however, by "digging" into the wall in a jump and popping it (the image of the monitor is a portion of the ‘zappers’).
	"S" monitor that does nothing. This monitor also appears in Sonic CD prototype 510, where it grants the player both extra speed and invincibility. That is most likely the intended function of the monitor here, as an issue of Computer & Video Games alludes to a powerup which grants extra speed and invincibility. This suggests that the "S" monitors were functional at that point in development. In the 2013 remake it can be placed and once destroyed you transform into Super Sonic regardless of how many Chaos Emeralds you have.
	The checkered ball seen on the Green Hill Zone Boss appears to have been originally used as a separate object in that zone, as magazine pictures have shown Sonic riding down hills on it. These can be seen in debug mode but not placed. Its associated code has been removed from the ROM.
	These spikes are horizontal, rather than the vertical spikes used in the final Marble Zone, and are also slightly thinner. However, they can be placed and are fully functional. The object ID is 45 in SonED2.
	Many early previews of Sonic the Hedgehog showed the text "PRESS START BUTTON" on the Title screen. In the final version it does not show up due to an in-game bug, but the graphics can be found inside the ROM. It is also possible to get them to display in the Japanese version: this occurs after accessing the secret credits screen via a cheat code (in emulators, the region of the emulator must be set to Japan), or an easier way is to enter the Game Genie code AB3A-DADV.
	The swinging platforms of Green Hill Zone will carry a wrecking ball when the highest bit of their subtype value is set. The object is fully functional, and can hurt Sonic. Technically, the swinging platforms of Marble Zone, Star Light Zone, and the swinging spikeball of Scrap Brain Zone are capable of doing this, too, but the wrecking ball graphics are not loaded, suggesting this feature was only intended for Green Hill Zone.

Warping effect

Thought to be the original method of accessing the special stage, this warp effect activates when Sonic touches the area in which the object is placed. Sonic disappears as he runs into it, and a warping noise plays. Sonic then reappears a few seconds later, likely as a method of testing the object.

Cheat device codes

These are cheat codes that can only be used with game enhancer devices. Support for these codes is available in most emulators.

Game Genie

Official codes

Code	Effect	Reference
ATBT-AA32	Master Code (Not needed in emulators).
AE3T-AACL	You start with 1 life.
AY3T-AACL	You start with 5 lives.
AE0T-CABE	Once you gain Invincibility, you stay invincible until the stage ends, or when you die.
AE0T-CABY	Once you gain Speed Shoes, you keep them until the stage ends, or when you die.
SCRA-BJX0	Each ring is worth 2.
SCRA-BNX0	Each ring is worth 3.
SCRA-BTX0	Each ring is worth 4.
SCRA-BYX0	Each ring is worth 5.
SCRA-B2X0	Each ring is worth 6.
SCRA-B6X0	Each ring is worth 7.
SCRA-BAX0	Each ring is worth 8.
SCRA-B9X0	Each ring is worth a crazy amount of rings.
GJ6A-CA7A	Infinite lives.
AJ3A-AA4G	Access to the Level Select menu.
AY3T-BA4R	Start with 5 Chaos Emeralds in possession.
DDLT-AAGL	Jump higher than your regular jump.
KDLT-AAGL	Jump lower than your regular jump.
BDLT-AAGL	Jump VERY high and "float" in the air.
NCLT-BYE6	Some Crabmeats go berserk.
NCLT-B9E6	Some Crabmeats disappear altogether.

Unofficial codes

Code	Effect
663T-BA4R	Max out score with one kill.
663T-B64R	Start with 2 continues.
A23T-BA4R	Start with all Chaos Emeralds.
AE2T-AAAL	Enable Debug mode.
GLRT-AADY	Ring count resets to 50 if Hit (Must have at least 1 ring).
NRRT-AADY	Ring count resets to 99 if Hit (Must have at least 1 ring).
AA2A-ACC8	Start on Labyrinth Zone.
AA2A-AEC8	Start on Marble Zone.
AA2A-AGC8	Start on Star Light Zone.

Action Replay

Unofficial codes

Code	Effect
00A35E:6042	Every Monitor Powerup gives Speed Shoes.
FFFE20:00C8	Infinite Rings (Turn off before passing end of level sign).
FFFE15:00FA	Never run out of air Underwater.
FFFE2C:0001	Always have Shield.
FFFE24:0000	Infinite Time.
FFFE2D:0001	Invincibility (Monitor Effect without speed boost).
FFFFD0:0100	Enable Stage Select (+ on Title Screen).
FFFE10:XXYY	Stage/Act Modifier (XX: Zone, YY: Level). 00 - Green Hill Zone 01 - Labyrinth Zone 02 - Marble Zone 03 - Star Light Zone 04 - Spring Yard Zone 05 - Scrap Brain Zone Note: Scrap Brain Zone act 3 is accessed by using level code 03 for Labyrinth Zone (i.e. it is treated as the fourth act of Labyrinth Zone). Final Zone is considered to be the third act of Scrap Brain.
FFD861:0001	Final zone's first boss health equals 1.

User-Found codes

Code	Effect
00D5CA:0005	Very Low Gravity
00CAA8:0532	Corrupted Spring Yard Title Card
FFF600:00YY	Game Mode Modifier (YY: Mode). 00 - SEGA Screen 04 - Title Screen 08 - Demo 0C - Level 10 - Special Stage 14 - Continue Screen 18 - Ending Scene 1C - Credits 8C - Pre-Level