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Sonic & Knuckles is a stand-alone expansion pack from Sonic the Hedgehog 3 that is a good game in its own right, but when combined with Sonic 3 becomes what could arguably be the best Sonic game ever.

• 6Unused Sprites
• 8Unused Zones
• 9Unused Areas
• 10Misplaced Objects

Level Select

The level select can be accessed by starting the game and grabbing one of the lifts in Mushroom Hill Zone. Once you have grabbed a lift, press Left, Left, Left, Right, Right, Right, Up, Up, Up. If done correctly, you should hear a ring chime.

When paused, you can perform the following actions:

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• A - Return to title screen.
• B - Play at half-speed.
• C - Advance by one frame.

Press Start to pause, then A to return to the title screen. At the title screen, press A + Start to access the level select. From there, you can press C to choose between Sonic (01) and Knuckles (03) only, and trying to select Sonic & Tails (00) or Tails (02) will give you Sonic alone. The Sonic 3 zones are also listed here, but choosing any of them will redirect you to Mushroom Hill. Entries in the sound test which will normally have songs only heard in Sonic 3 and Drowning are empty and unplayable.

Notes about the levels:

• Lava Reef Act 3 goes to the boss room. Knuckles cannot select this level.
• Lava Reef Act 4 goes to Hidden Palace Zone. Each character goes to their respective entrance in the level.
• Sky Sanctuary Act 1 is Sonic's level and Act 2 is Knuckles'. Sonic cannot go to Knuckles' level and vice-versa.
• Knuckles can enter Death Egg, but he cannot defeat the Act 1 boss (he cannot jump high enough to hit the boss in the first phase).
• If Sonic beats The Doomsday Zone, the bad ending will play if you don't have all the Chaos Emeralds.
• The Doomsday Act 2 leads to the final boss of Death Egg. If Knuckles defeats the boss, the game will reset to the SEGA screen.
• Knuckles cannot enter either level of The Doomsday.
• Bonus 1 goes to the Glowing Spheres game. Bonus 2 goes to the Slot Machine game. Finishing each stage will restart it.
• The only remnants of the Sonic 3 zones are the patches made to various zones. These still rely on the data from Sonic 3.

Debug Mode

Debug mode cannot be unlocked by normal means. It can only be unlocked using two means:

1. By using the Game Genie code RFTT-A6XW, then pressing A + Start on the title screen or when in the level select.
2. By utilizing a glitch in Sonic 3 & Knuckles whereby placing a long string of 'S' monitors in a row using debug mode, followed by spindashing into them, will cause the game to crash with a garbled screen. Pressing the Start button on this screen will load Sonic & Knuckles with level select and debug mode enabled. Using the Wii Virtual Console's 'Lock-on Menu', it is shown that the game still thinks that it's locked on to Sonic 3.

When in debug mode there, you can enter both normal and edit mode in-game. Normal mode is similar to normal gameplay but with added debug features, while edit mode is a mode where you can place objects anywhere in the level.

When in normal mode:

• Press A to reverse gravity (reaching the top of the level will kill you as if you fell off a bottomless cliff).
• Press B to enter edit mode.
• Press B + C to play through all the frames of the current characters' animations. (May work in edit mode, needs testing!)

When in edit mode:

• The coordinates of the current object are shown by the top line of hex digits in the HUD.
• The coordinates of the current viewport are shown by the bottom line of hex digits in the HUD.
• Press A to cycle forwards through the object list.
• Press A + C to cycle backwards through the object list.
• Press B to enter normal mode.
• Press C to place the current object shown.

You can use debug mode to enter any level a character would normally not be able to enter (see above), though in some cases this causes player sprites to become corrupted.

Entering edit mode during some parts of the game (such as the light tubes in Death Egg) will crash the game.

8th Special Stage

If Sound Test is enabled, and any of the Special Stage options is selected, Sonic or Knuckles is taken to the 1st Special Stage. The end of it however, spawns a Yellow Super Emerald. This is when the Special Stage is marked as clear, but the normal Chaos Emerald amount doesn't rise. The Super Emerald amount will rise, but it has pretty much no effect due to Super Emeralds being unobtainable. This bug will allow access to a hidden Special Stage and allow for the 8th Emerald to be collected once the other six have, though.

It is also possible to access this Special Stage by enabling debug mode above, then setting the Sound Test selection to 07 and pressing A + Start while selecting any of the Special Stage options.

Tails

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As with Knuckles being unavailable in Sonic 3 but with a few leftovers, Tails is not available in this game. Unlike Knuckles in Sonic 3, however, he is in an actual playable form! Unfortunately, most of his sprites are missing and are replaced with corrupted graphics.

If the Pro Action Replay code FFFF09:02 is used in Sonic & Knuckles, Tails will be usable, but just about every sprite of his except the transformation sprite will be missing, basically rendering him invisible (unlike when a savestate is used; a different, glitchy sprite is used in place of Tails' original one). There are four exceptions:

1. Tails' sprites used at the end of Sky Sanctuary Zone to run around the collapsing pillar are actually stored in the S&K ROM, and therefore are visible. The same sprites are also used in the same context in Lava Reef Zone.
2. Tails' hanging sprites from Sky Sanctuary are also visible.
3. Tails hanging onto the mushroom paragliders in Mushroom Hill Zone.
4. In Tails' bad ending, you can see him normally when he and Sonic fly away from the island.

Hidden Palace's Hidden Area

There's a hidden area in Hidden Palace Zone that is only accessible by debug mode or having Tails in Sonic 3 & Knuckles.

Just before entering the inside of Hidden Palace, fly from the two steps left until a ledge is reached. Walk left and six power-up monitors will appear, mostly shield monitors (Ring, Bubble, Fireball). In some of the S&K prototypes, an 'S' monitor is present instead of the Speed Shoes.

If you run right, leap off the ledge, and keep running right, you will find two Ring monitors and a 1-up monitor.(video)

Unused Sprites

Hidden Message in Slot Machine Bonus

Japanese characters are used as placeholders for slots animations. Read from top to bottom and from left to right, they are the first few parts of the Iroha poem.

Unused Music

A short 'Game Clear' jingle heard by playing sound 32 in the Sound Test. Though Sonic 3 used this sound ID for its own jingle played after defeating the final boss, it isn't used in Sonic & Knuckles at all. A longer version of this jingle can be heard at the end of the credits medley, though.

Unused Zones

There are a few acts that go unused.

The True Doomsday Act 2

Contrary to what the level select would lead you to believe, the real Doomsday Act 2 is inaccessible by normal means (unless a glitch is used or using patch code FFFE10:0C01). The level is basically empty except for some chunks off-screen. Super Sonic dies shortly after transformation due to being given 0 rings at the start of the level.

Slot Machine Bonus Stage Act 2

Basically the same as the regular version.

Glowing Spheres Act 2

The only major difference is the different spawn point, which places you inside a wall.

ID 0D Act 1

Crashes on entry, presumably before the title card even loads. This zone uses Angel Island graphics (which are non-existent in S&K) as a placeholder, which is one of the reasons the Act crashes. The only thing this act is ever used for is giving Hidden Palace its own title card. In Sonic 3, this zone has its own unique ring layout, possibly suggesting it was something entirely different at one point in development. For reference, ID 0D Act 2 is the ending sequence for Sonic.

Gumball Machine Bonus stage

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This bonus stage was in Sonic 3 (alone) and in Sonic 3 & Knuckles. It goes absent in this game and simply crashes on the title card.

Unused Areas

Lava Reef Zone Act 1

There are three empty bonus rooms in Lava Reef Act 1. They appear to have been used to hold Special Stage rings at some point in development. Inside, there are tunnels that would have allowed you to enter and exit them, except that they have been blocked off by invisible solid objects. They appear to be remnants from an early version of the stage, like the one that was restored from the Sonic 3 Nov 3rd, 1993 prototype. The locations are as follows:

1. To the right of the first Spin Dash elevator at coordinates 09C005C0.
2. To the right of the Spin Dash elevator encountered after the driller badnik, at coordinates 13C00740.
3. Beneath the crushers on the top path shortly after Sonic's path splits into two, at coordinates 21400540.

Death Egg Zone Act 1

At the top of the first wide conveyor belt elevator sequence in the Act is a hidden room containing two ring monitors and an invincibility monitor. However, the corridor leading to the room is completely blocked off by spikes, making the room impossible to get into without debug mode.

Misplaced Objects

Flying Battery Zone Act 1

There are two yellow springs buried in the ground near the first giant purple tube.

Mysterious spikes are hidden in the floor of Flying Battery Zone 1.

Death Egg Zone Act 1

There are three rings placed in the floor under the first black antigravity ball. It is possible to collect these rings by returning to this point with a Lightning Shield.

Sonic 3 Level Select Code

The Sonic 3 level select code... code is still present in the ROM and can be reactivated via hacking. Interestingly, it was updated to work on the Sonic & Knuckles title, and to be inputted at all times in the Sonic 3 title (unlike Sonic 3 Alone, in which you can only input it after the Sega logo but before the title screen appears, which is made harder via the ridiculous number of lag frames).

This is a sub-page of Proto:Sonic & Knuckles.

Sonic 3C 0408 is a prototype for a canceled Sonic 3 and Sonic & Knuckles compilation that would have been called Sonic the Hedgehog 3: Limited Edition. When this prototype was obtained by drx, the file was labeled '3C', indicating this was an unreleased version of Sonic 3. Due to the late development date, it's obvious this isn't Sonic 3 before it was split into two games.

• 3Zone Differences
  • 3.15Bonus Stages
  • 3.16Special Stages
• 5Unused Level Chunks

Cheat Codes

Level Select is enabled by default, so you can just go down to Sound Test at the title screen.

In the Sound Test, you can enter the following combinations:

• 01, 03, 05, 07 - Enables debug mode.
• 02, 04, 06, 08 - Get all the Chaos Emeralds.

You can also use patch codes FFFFE2:0001 and FFFFFA:0001 to enable debug mode.

General Differences

Note: S3 = Sonic the Hedgehog 3, S&K = Sonic & Knuckles

• Knuckles is selectable in 1-Player mode.
• Some of Super Sonic's sprites are garbled when interacting with certain objects in the S&K zones.
• Tails and Knuckles have incomplete Super forms, since the art has yet to be implemented, thus Knuckles cannot turn Super by normal means. Likewise, Hyper Sonic is not in the game yet.
• Due to Hyper Sonic not being in the game yet, 'S' monitors will only transform you into Super Sonic, and will still play the incorrect sound effect like in Sonic 3.
• The ending sequences have yet to be implemented.
• No glowing Special Stage rings are present in the S&K zones.
• The save format is identical to the one found in Sonic 3. You can play a saved game past Launch Base Zone, but when you exit the game, the save will be indicated as 'Clear', and only Zones 1 through 6 can be selected. There are also only 6 save files as opposed to 8 in Sonic 3 & Knuckles, and lives and continues are not saved or shown. (The final Sonic 3 actually had 14 save images; 6 for S3 only, 8 for Sonic 3&K.)
• Knuckles has a different underwater palette.
• The music for the title screen, mini-bosses, Knuckles, invincibility, and collecting 1-ups are all from Sonic 3.
• The Data Select music bug from Sonic 3 alone is still there.
• The Super Sonic water shield bounce glitch from Sonic 3 is still present.
• Pressing A while the game is paused returns you to the level select screen rather than the SEGA logo screen.
• Many sound effects are missing, especially in the Sonic & Knuckles Zones and when playing as Knuckles.
• Monitors placed with debug are Lightning Shield monitors, rather than Super Sonic monitors.
• Blue Knuckles still appears on the goal signpost when playing as Sonic or Tails. Likewise, a red Sonic is shown on the signpost when playing as Knuckles.
• Monitor behavior is the same as in Sonic 1-3 in this build, where you have to jump on a monitor to break it, and hitting it from underneath makes it fall.
• The following levels cannot be accessed in the level select. Enabling debug mode removes these restrictions, allowing you to enter them:
  • Lava Reef 3 & 4 (Act 2 Boss & Hidden Palace)
  • Sky Sanctuary 2
  • The Doomsday 1 & 2 (Doomsday & Death Egg Final Boss)
  • Bonus 1 & 2 (S&K Bonus Stages)
  • Special Stage 1 & 2
• On a Japanese system, the trademark symbols are not removed from the SEGA logo and title screen, and Tails' life counter does not become 'Miles' even though the results tally changes to 'Miles'.

Zone Differences

Angel Island Zone

• Act 1 will still play Act 2 music when returning from a Bonus Stage after the Zone has been set on fire, like in Sonic 3.
• Knuckles can't shatter the rock that allows access to Sonic's path, and because of this he can take that route. However, the boss always spawns in Knuckles' path, causing him to become stuck.
• Knuckles' route in Act 2 still has its object layouts from Sonic 3.

Hydrocity Zone

• Knuckles' route in Act 2 has no rings, enemies, or checkpoints.
• When fighting the Big Shaker, the game plays the Sonic 3 mini-boss theme instead of the Act 2 boss theme (Sonic 3 final plays the Act 2 boss theme, but switches to the Sonic & Knuckles mini-boss music if the drowning timer starts and you get out of the water; Sonic 3 & Knuckles final plays the Sonic & Knuckles Act 1 mini-boss theme.)
• The spring that sends you backwards at the beginning of Act 2 is replaced with a 1-Up, which is the same as Sonic 3 & Knuckles final but not Sonic 3 final.
• The Screw Mobile's twister can still glitch out Super Sonic like it did in Sonic 3.

Marble Garden Zone

• The Act 1 miniboss crash glitch from Sonic 3 that can be achieved with a second player is still present.
• The start of Sonic's segment in Act 2 does not have a wall to prevent Knuckles from defeating the Relief, and instead has an extra set of spikes. Knuckles can hurt himself, stand on the spikes during the brief moment of invulnerability, then jump into the Relief's eye and destroy it, allowing access to Sonic's segment.
• Knuckles can climb on walls during the moving walls sections in both his route and Sonic's.

Carnival Night Zone

• When playing as Sonic alone in Act 1, Tails randomly appears after the boss. (This randomly happens in the completed Sonic 3, but with a different frequency.)
• Knuckles does not run in at the start of Act 1,
• Knuckles' route in Act 1 still has its object layouts from Sonic 3.
• Knuckles can climb the walls during the Bowling Spin boss fight. In the final version, he can't.
• In the room where Knuckles would go through the breakable wall to his own path in Act 2, there is still a spinning barrel. This was removed in later prototypes and the final and replaced with spikes to stop Knuckles from taking Sonic's path instead.
• Knuckles' route in Act 2 does not end with a Prison Egg, but the teleporter that goes to IceCap Zone is functional, anyway.
• When playing the game normally as Knuckles, after you defeat the Act 1 boss, the game freezes a few seconds after the signpost lands and after Knuckle's victory animations.

IceCap Zone

• In Act 1, when Tails first descends while playing as Sonic and Tails, the graphics are screwed up: the snowboard intro overwrites Tails' tiles with the snowboard's, and when the snowboard disappears, Tails' tiles should load. However, Tails' AI doesn't allow this to happen fast enough, and thus proceeds to draw Tails with some of the snowboard's tiles still remaining. Only when Tails lands does the tile swap complete, and Tails return to normal.
• The floating icicle spheres in one of Knuckles' routes can hurt Super Sonic, just like they did in Sonic 3.

Launch Base Zone

• The background in Act 1 is a little glitchy.
• The object layouts for both Acts have been changed to the ones seen in Sonic 3 & Knuckles.
• The elevator poles at the end of Act 1 are not removed when playing as Knuckles.
• As soon as Knuckles defeats one of the Twin Hammers, the normal Act 1 theme resumes while the other Twin Hammer is still alive.
• A suspension pole near two submerged teacup elevators near the end of Act 2 isn't solid. It was made solid in later prototypes and the final to prevent Knuckles from riding the elevators and taking Sonic's path.
• Knuckles does not fight the Big Arm at the end of Act 2, and the boss music does not stop playing when the Prison Egg appears.
• The bubble graphics in Act 2 appear glitched.
• Sonic no longer fights the Big Arm at the after the Laser Columns boss.

Mushroom Hill Zone

• The level layout of both Acts is different, and the differences are very noticeable at the start of Act 1. Knuckles starts at the top of the level with Sonic and Tails starting lower down instead.
• Sonic and Tails just drop down in their standing poses instead of Tails lifting Sonic into the Zone.
• Knuckles does not run into any giant rings at the start of his Act 1.
• The giant ring in Sonic's area in Act 1 does not flash.
• If you enter the aforementioned giant ring without all the Emeralds, you'll be sent to the Hidden Palace chamber with Death Egg Act 2 music playing, then instantly warp to a different Special Stage.
• One bonus room in Act 1 contains a diamond cluster of rings. It was changed to a giant ring later in development.
• Hei Ho's axe can hurt you.

• The lever that Knuckles pulls down repeatedly in Act 2 has a blue handle. In Knuckles' game, the lever doesn't appear at all.
• A giant ring at the start of Sonic's Act 2 (after the Knuckles cutscene) is missing and has a bit of Russian Roulette action in its place. There are two monitors wedged in the ceiling, and one of them is a 1UP monitor while the other is a Robotnik monitor.
• There is no giant ring near the pulley that takes you to the boss in Act 2.
• The Act 2 boss's starting position is shifted to the left slightly from the final. This allows you to score endless hits on the boss without destroying the satellite, and the battle won't start until you hit the satellite itself, thus it was changed in the final so the player cannot do this. These hits also don't count toward defeating the boss.
• The Act 2 boss does not explode when killed until he crashes into the tree, and you must hit him six times after he has zoomed off.
• During the transition to Flying Battery with Sonic and Tails, Tails won't stop running to the right and will kill himself in the pit.

Flying Battery Zone

• The echo track of Act 1's music will go off-sync after looping, and will slowly drag more and more behind the lead melody as it continues to play.
• Various objects are missing in some places, such as badniks, hooks and rings.
• There are no giant rings in either Act.
• Some of the magnetic platforms are embedded in spikes. They can still hurt you if the platform isn't raised.
• Gapsule's position is about 16 pixels to the left in comparison to later prototypes and the final. The coordinates are the same as in Sonic 3.

• A double set of doors in Act 2 does not open completely.
• A few level design differences. For example, the pendulums in Act 2 are missing, and in the area after the Act 2 miniboss, there are two ring monitors in place of a red spring, and there are no spikes.
• Some of the elevator shafts do not have spikes, and some that go upwards do not crush the player at the ceiling, instead pushing them through it.
• There is an erroneous chunk placement in the background near the end of Act 2.
• Robotnik stops exploding as soon as he begins to fly away.
• Your character does not automatically roll when he busts down the door during the transition to Sandopolis Zone. They appear to be rolling in the Sandopolis intro, though.

Sandopolis Zone

• Your character enters Act 1 in a rolling state, but does not get stuck in the sand. The controls aren't even locked at all, meaning you are permitted to move left or right before you land.
• Some more object layout differences.

Sandopolis Zone Act 1

• The first of Knuckles' alternate routes in Act 2 does not lead to the sand slides, instead forcing you to drop back down into Sonic's route.
• The rising sand in Act 2 rises more slowly.
• In the rising sand sections, all three shields and a 1-UP are tucked away in a corner. They are later replaced with a Super Ring and a Super Sneakers monitor.
• The area where there would be a very long slide in the final is very different. It is a series of slides which also includes a loop-de-loop that uses level chunks which are completely absent in later prototypes and the final.

Sandopolis Zone Act 2

Lava Reef Zone

• Even more object layout differences.
• Knuckles doesn't run in at the start of Act 1. He just stands there.
• Knuckles can destroy the four pistons of the driller robot by gliding into them before it begins drilling.
• Shields do not protect you from the debris of the exploding rock badniks.
• The bonus monitors at the end of Act 1 are visible for some reason, and for some stranger reason, the monitors have reversed gravity when released by the goal sign. When Act 2 begins, any monitors that have gone off the top of the screen can be seen underneath the ground.

• The lava at the end of Act 1 does not cool when Act 2 begins, but you can still walk on it.
• Act 2's palette has yet to be changed to indicate a freeze-over.
• The screen does not lock behind your character after having passed the first flamethrower.
• When you encounter Knuckles, his theme does not play, and he laughs after punching the boulder at you. The boulder doesn't make any sounds and won't cancel your Super form.
• The Act 2 boss area does not play the boss theme at the start. It plays it as soon as the boss emerges from the lava.
• The Act 2 boss area does not have a Lightning Shield. The ring pattern is also different.
• The lava in the boss area does not cool after breaking the Prison Egg. Instead, once the results tally has finished, the platform you're standing on will drift to the right a bit, then you'll have to jump across more platforms as the lava can still hurt/kill you. The level music does not resume, either.
• The tunnel at the end of Sonic's Act 2 does not go to Hidden Palace, so you're basically stuck. Knuckles' exit to Hidden Palace works, though.
• Without debug mode, the boss area cannot be accessed directly from the level select.

Hidden Palace Zone

• This Zone does not play Lava Reef Act 2's music, but Sky Sanctuary's.
• The title card refers to this zone as Sky Sanctuary Zone Act 1.
• The player does not run in at the beginning.
• The screen locks the way back to the starting area after you pass the first set of spikes. The lock is set to happen at X coordinate 0500 where a foreground palette change from purple to green would occur.
• A Fire Shield is present in place of a Ring monitor, near the teleporter that leads to Knuckles.
• In the hidden area, there's a Super Sonic monitor instead of a Ring monitor, and three 1-Up monitors instead of one. As debug mode places Lightning Shields instead of 'S' monitors in this build, this is the only 'S' monitor in the game.
• The hole in the background isn't properly lined up with the teleporter before the Knuckles fight.
• The above-mentioned palette change screws up if you enter a Bonus Stage and come back, causing areas to be purple when they shouldn't be (e.g. the teleporter and the Master Emerald's altar).
• The Knuckles battle plays the Sonic 3 miniboss music. After defeating Knuckles, the music doesn't stop, and continues to play through the Master Emerald theft scene.
• Knuckles can hurt you when you have any form of invincibility state, including invulnerability states after getting hit, an invincibility powerup, and Super Sonic. He can even hurt you if you're in debug mode placing an object, at which point Sonic's graphics might be corrupted.
• Beating Knuckles does not cancel your Super form.
• At the start of the Master Emerald theft scene, Knuckles just stands on the ground looking upward as Robotnik pulls up the Master Emerald. When Robotnik attempts to escape, Knuckles doesn't hit him, and just grabs on to the emerald.
• The controls are locked with Sonic looking upward when Robotnik shocks Knuckles, but if you use debug you can remove the control lock, though you can't hit Robotnik and you can stand on top of the Master Emerald.
• After regaining consciousness, Knuckles will charge through the breakable wall, rather than stopping in front of it and punching it.
• When you approach the teleporter that leads to Sky Sanctuary, there is no cutscene. The controls and camera won't lock, and Knuckles won't jump on the teleporter. You can stand on it to activate it, anyway.
• This Zone cannot be accessed in the level select without enabling debug mode.

Sky Sanctuary Zone

• Once again, more level layout differences.
• Both Sonic's and Knuckles' versions of this Zone are considered to be Act 2 as the above Zone counts as Act 1.
• The air ducts are not active while Knuckles is en-route to enable the bridge in Sonic's Act, allowing the player to die by mistake.
• There seems to be some palette conflicts.
• The bouncy clouds don't seem to animate.
• The screen lock works differently in the Green Hill Zone boss fight, and the teleporter emerges in different positions.
• After the Metropolis Zone boss has been defeated, the balloons don't pop until they reach the ground.
• After beating the Green Hill and Metropolis bosses, the timer freezes and Sonic loses the ability to turn super. Dying or entering a Bonus Stage fixes the problem.
• After defeating Mecha Sonic at the end of Sonic's Act, the game cuts straight to Death Egg Zone with no results tally or cutscene.

Sky Sanctuary Zone Act 1

• Knuckles' Act does not have any rings, and the teleporter is absent.
• Pausing and returning to the Level Select from Knuckles' Act messes up the Level Select background slightly.
• As soon as the final boss theme plays, the normal Act 2 boss theme starts up again.
• Doomsday Zone music does not play in the second half of Knuckles' final boss fight.
• The screen does not flash when Mecha Sonic becomes Super Mecha Sonic.
• Some of Super Mecha Sonic's poses are a bit different.
• When Super Mecha Sonic is defeated, he does not land on the ground and drops off the screen, and nothing else happens after that.
• The Floating Island overlaps the Master Emerald.
• Knuckles' Act 2 boss fight behaves normally as Knuckles, but if loaded as Sonic or Tails, the boss will be very broken. It seemed to have been used as a test.

Death Egg Zone

• The player does not run in at the beginning.
• The overscan border color for Act 1 is red, instead of black like the other zones.
• There are a few object layout differences, with notable ones being the absence of rings and monitors in some bonus rooms.
• Many sound effects are missing, and the missile launchers play a different sound when firing.
• Red Eye's pillar overlaps the player and has tile transparency issues.
• The explosions seen when Red Eye moves to phase two last longer than usual.
• Red Eye's laser overlaps the floor.

• The palette changes too soon when transitioning to Act 2. In Sonic & Knuckles 0525 and later, the palette is changed after the Act 2 transition completes.
• If the signpost has been hit before landing, it'll fall at an angle when the floor explodes during the Act 2 transition.
• Tails has an animation error during the Act 2 transition.
• Act 2 ends with a Prison Egg after the Act 2 miniboss is defeated, then the player moves on to The Doomsday Zone, regardless of whether or not they have all of the Chaos Emeralds.
• The final boss (accessible by selecting Doomsday Act 2 in the level select with debug mode active) is really incomplete, only having a background, a few rings, no title card, and various poses of the final boss laid out throughout the act. There's nowhere to stand on, so you'll fall and die over and over.
• There is also a prototype floor tile that is not seen in the final game located in the final boss area:

The Doomsday Zone

• Really incomplete, only having the boss graphics and a background with no Super forms available, so you'll just fall to your death repeatedly. You can use debug mode and fly over to a section with glitchy collision.
• The background palette is the same as in Death Egg Zone Act 2.
• The HUD and ring palette is incorrect here.

Bonus Stages

At this point in development, the Sonic & Knuckles bonus stages are very unfinished. In normal play, Starposts will randomly send you to either the Gumball Machine or the Slot Machine when you hit it with at least 50 rings. The color of the stars is always white.

Glowing Spheres

• This Bonus Stage is vastly incomplete, and thus does not appear in normal play. The only way to access it is via level select with debug mode active.
• No collision, partially complete graphics, and a preliminary animating background. As a result, you can only really die there.
• Since the graphics are partially complete, there are some that don't even appear in the final.
• The palette for this Bonus Stage is exactly the same as the one in Sonic 3, and does not cycle.

Slot Machine

• The layout is vastly different, with more rings (a total of 64 compared to S&K Final's 24) and no GOAL blocks when starting the level (the borders still turn into GOAL blocks, though).
• The background is completely static. The little objects don't rotate and nothing scrolls.
• There is a higher chance of getting 3 Robotnik pictures on the slots than in the final version.
• Using debug to fall out of the stage causes the game to crash. In the final, it takes you to a glitchy area with randomly placed tiles, a la Sonic 1.

Special Stages

The Special Stages for the Super Emeralds are completely different from Sonic & Knuckles. The colors are exactly the same as the Special Stages of Sonic 3, but the sphere arrangements are completely different. Some of these layouts would become different Special Stages, and some would be outright dropped altogether. For example, the planned third Special Stage in 3C became the hidden eighth in Sonic & Knuckles.

Special Stage 1

Special Stage 2

Special Stage 3

Special Stage 4

Special Stage 5

Special Stage 6

Special Stage 7

This version uses the exact same object layout as the seventh Special Stage as Sonic 3's. It might have been just a carryover given the nature of development both games share.

Special Stage 8

Unused Graphics

Sonic And Knuckles Slot Machine Free Play

Unused Level Chunks

Several level chunks aren't used, but can still be seen in the game data.

Flying Battery Zone Act 1 & 2

• CA

• D3

Lava Reef Zone Act 1

• E2

Lava Reef Zone Act 2

• 1F

• 20

• 47

• 4A

• 4B

• 87

Hidden Palace Zone

• 18

• 43

• 5D

• 75

Sonic And Knuckles Arcade

Sky Sanctuary Zone

• 4C

• 50

• 89

Sonic And Knuckles Slot Machine Machines

Death Egg Zone Act 1 & 2

Sonic And Knuckles Slot Machines

• 63

• 64

• 66

• 67

• B6

• B7

• E0

• E5

Sonic And Knuckles Download

Sonic 3 Ending Leftovers

The Big Arm final boss from Sonic the Hedgehog 3 is still completely intact and can be hacked back into the game. The boss behaves as normal and is able to be defeated. Once this happens, the ending from Sonic the Hedgehog 3 takes place and the credits begin. However, since Knuckles is here this time, he has his own broken ending. Knuckles uses all his correct poses until the giant Sonic sprite shows-up which causes Knuckles's palette to get messed up. For some reason, the screen fades to the credits a good bit faster than it does for Sonic & Tails. This could be a possible leftover from an incomplete ending for Knuckles in Sonic 3.