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Proto:Sonic the Hedgehog 2 (Genesis)/CENSOR Prototype

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This is a sub-page of Proto:Sonic the Hedgehog 2 (Genesis).

Hiddenpalace.org logo.png  This prototype is documented on Hidden Palace.

STH 2 Prototype Beta 4 Title.gif

This build of Sonic the Hedgehog 2 was originally released by the scene group CENSOR on November 9, 1992, about two weeks before the final game's release. The build was quickly forgotten in favor of a dump of the final game by fellow group MAGICAL, partly because at the time nobody wanted pre-release builds of games (yes, really). It wasn't until February 14, 2019 that the build was rediscovered by drx and Evilhamwizard before subsequently being released through Hidden Palace.

Download.png Download Sonic the Hedgehog 2 (CENSOR prototype)
File: Sonic The Hedgehog 2 (CENSOR Prototype Hack).bin (1 MB) (info)


Notes on the game's internal data.

General Differences

  • The ROM's header was edited to make it easier to identify in a copier, with the most notable change being that the serial code was changed to Wani Wani World's, and an additional demoscene intro was added. The download above has been modified to remove these changes and restore the ROM to its original state.
  • Tails is always called Miles regardless of the region.
  • The title screen and level select remain identical to previous builds, though selecting "2 PLAYER VS" sends the player to the proper 2-player level select.
  • Debug Mode is enabled by default, and can be accessed by holding A while selecting a level.
  • For some strange reason, edit mode has been disabled and only debug information appears. Use Pro Action Replay (PAR) code FFFE08:0001 to activate edit mode.
  • Path swappers (which are used by the engine to switch Sonic onto another plane) are no longer visible in Debug Mode, like the final game.
  • Music now plays at the same speed on European consoles as it does on others.
  • Slope collision in this build is different compared to Beta 4, as Sonic acts like he's on flat ground when he's standing on a slope. The collision is also less lenient, as Sonic gets crushed in areas he can't be in the final game (e.g.: under Chemical Plant's tubes).
  • The death function is bugged somehow, as the screen no longer locks when you die. This wasn't fixed until Beta 6.
  • The infamous Sonic 1 spike behavior (where spikes ignore invulnerability frames after being hit) is still present, something that wasn't changed until Beta 5.
  • End-of-Act results have a period between "Act" and "1/2". This detail was removed in the final.

Ledge Sprite Detection

In all zones that have ground tiles, there seems to be a problem with how it detects where Sonic is standing on the platforms. If you go near the end of a right hanging platform, Sonic will instead float and not go to his losing balance sprites. This only seems to work on right hanging ledges while the left ones are working as they should be in the final build. This does not work with sprites.

CENSOR-Beta 4 Beta 5-Final
Sonic The Hedgehog 2 CENSOR Prototype Hack.png Sonic the Hedgehog 2 Prototype Beta 5.png

2-Player Mode

Nearly complete, with only a few bugs left:

  • Tails' shield doesn't display.
  • Eggman monitors don't harm the players yet. Fixed in Beta 6.
  • If either player gets a Time Over, the stage will reset and then immediately go to the results screen. This sets their score, time, ring, total ring, and item box numbers to what they were the last time they hit a checkpoint - or, if they never hit a checkpoint, to zero. Fixed in Beta 6.
    • Getting a Time Over in 2-Player will play music track $8F, which was the Game Over track in Sonic 1 but is now the Wing Fortress theme. This is odd considering every other Game/Time Over screen properly plays track $9B.
  • The results screen for the 2-Player Special Stages always shows Special Stage 4, regardless of which one you just played. This was fixed in Beta 6.
  • There's no countdown if a player passes the signpost.

Super Sonic

Super Sonic has been partially worked on since September 14th, but is still far from completion.

  • In previous builds the player could activate Super Sonic by placing a "?" monitor in Debug Mode, but since it has been removed, cheats are now required. Use Pro Action Replay (PAR) code FFF65F:0001 to enable the Super Sonic palette, FFFE19:0001 to enable the Super Sonic sprites and increased jump height, and FFB02B:0006 to enable invincibility and Speed Shoes.
  • Super Sonic still has no underwater palette. This was partially fixed in the final game when Sonic transforms above water, but transforming underwater still causes Sonic to use the above water palette.
  • Super Sonic doesn't produce any sparkles while going fast.
  • The increased speed and acceleration are not enabled (this is set by the transformation sequence in later builds), but the player can get the increased speed/acceleration if they either get a Speed Shoes monitor and let it expire, or go into the water and then jump back out.
  • If Super Sonic is about to drown and then gets out of the water, the invincibility music will play.

Zone Differences

To do:
Compare level layouts between the September 14th and Beta 4 builds.


Sky Chase & Wing Fortress
A little was done between builds.
Death Egg and Hidden Palace
Are you down yet?

Chemical Plant Zone

  • This is the final build to have hexagonal loops. They were changed to be fully square as running on them causes Sonic to die.

Casino Night Zone

Sonic2CENSORCNZ2 10rings.png

An unreachable 10-ring monitor is present in Act 2 below the ground near the start. This was removed in Beta 5.

Metropolis Zone

  • Finishing Act 2 takes you directly to Sky Chase instead of Metropolis Act 3. If you use the level select to play Metropolis Act 3 and then finish it, the game will take you to Aquatic Ruin Act 1.

Hidden Palace Zone

The tile and collision data belonging to the zone appears removed at this point, though Redz badniks that have managed to find solid terrain will still be visible. The music for this stage, at this point, has been changed to sound test #10.

CENSOR PROTO Redz badnik.png

Special Stages

Significantly further along than September 14th, but still incomplete.

  • Like the previous build, Special Stages take a long time to load. See the September 14th page for more info.
  • Rings were removed at the end, as they flashed rainbow due to the palette change.
  • After the first round of a Special Stage in 2-Player Mode, the "Most Rings Wins!" message changes to "Win Twice Win All!". This message was removed in Beta 5 for unknown reasons.
  • The stages have different palettes to the ones used in the final, though the palettes for Stages 1, 3, and 5 were eventually reused for Stages 2, 5, and 7 respectively. These palettes are also in Betas 4 and 5, but the stages use their final palettes from Beta 6 onwards.
CENSOR-Beta 4 Beta 6-Final
Sonic2Beta4 SpecialStage1.png Sonic2 SpecialStage1.png
Sonic2Beta4 SpecialStage2.png Sonic2 SpecialStage2.png
Sonic2Beta4 SpecialStage3.png Sonic2 SpecialStage3.png
Sonic2Beta4 SpecialStage4.png Sonic2 SpecialStage4.png
Sonic2Beta4 SpecialStage5.png Sonic2 SpecialStage5.png
Sonic2Beta4 SpecialStage6.png Sonic2 SpecialStage6.png
Sonic2Beta4 SpecialStage7.png Sonic2 SpecialStage7.png
(Source: Hidden Palace, TCRF original research)

Sound Differences

The sound driver has been improved vastly from the previous build, and now plays music at the proper speed on PAL consoles.

Sound C0

A new sound was added in the slot of Sound C0, instead of it playing a flapping sound as heard in September 14th, it now plays a sound intended for the slots in Casino Night Zone, although wasn't used until Beta 4.

CENSOR - Beta 4 Beta 5 Onwards

Sound EF

Sound EF ends differently. It wasn't used until Beta 5.

CENSOR - Beta 4 Beta 5 Onwards
File:Sonic 2 CENSOR Prototype Sound EF.ogg File:Sonic 2 Beta 5 Sound EF.ogg


To do:

On demos, there is a glitch that makes Sonic invisible, messes up the camera and duplicates rings. After performing the bug, the camera moves slowly on the X axis, Tails' AI gets messed up and some objects turn invisible along with Sonic. Even the 2 player demos have this same bug, with the difference being that Tails' AI doesn't screw up.

Yes, that's how it behaves