Sonic & Knuckles

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.

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Level Select/Debug Mode

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

When paused, the following actions can be performed:

• 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, pressing C can choose between Sonic (01) and Knuckles (03) only. Trying to select Sonic & Tails (00) or Tails (02) will just give Sonic alone. The Sonic 3 Zones are also listed here, but choosing any of them will redirect to Mushroom Hill. Entries in the sound test which normally have songs only heard in Sonic 3 are now empty and unplayable.

Notes about the levels:

• Lava Reef Act 3 goes to the boss room. Knuckles can't 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 can't go to Knuckles' level and vice-versa.
• Knuckles can enter Death Egg, but can't defeat the Act 1 boss (Knuckles is unable to jump high enough to hit the boss in the first phase).
• If Sonic beats The Doomsday Zone, the bad ending plays if the player doesn'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 can't 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:

1. By using the Game Genie code RFTT-A6XW then pressing A + Start on the title screen or when in the level select, or the Pro Action Replay (PAR) code FFFFFA:0001 which enables debug mode without the need of a button combination.
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 most often cause the game to crash with a garbled screen (though sometimes it will only revoke player control, and other times the player can still play in the Sonic 3 Zones until exiting the stage). Pressing the Start button in the first two states (Start + A if Controls haven't been revoked) 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. Likewise, Sonic Mega Collection will also think the same.

When in debug mode, it's the same old songs and dances as the last three games. Normal mode is similar to normal gameplay but with added debug features, while edit mode is a mode where objects can be placed anywhere in a level.

When in normal mode:

• Press A to reverse gravity (open ceilings act as death pits).
• 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 return to normal mode.
• Press C to place the current object shown.

Having debug mode enabled disables the lock that prevents Sonic/Knuckles from going into each other's exclusive levels (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, and moving far in Flying Battery from the player's death location) will crash the game.

8th Special Stage

If Sound Test is enabled, and any of the Special Stage options are selected, Sonic/Knuckles will be taken to the first Special Stage. The end of it spawns a Yellow Super Emerald however. 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 in Sonic & Knuckles standalone. This bug will allow access to a hidden Special Stage and for the 8th Emerald to be collected once the other six have though.

It's 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

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's in an actual playable form! Unfortunately, most of his sprites are missing and are replaced with corrupted graphics.

If the Pro Action Replay code FFFF09:0002 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 Sonic & Knuckles 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, he can be seen normally when Tails and Sonic fly away from the floating 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 Sonic & Knuckles prototypes, an "S" monitor is present instead of the Speed Shoes.

Two Ring monitors and a 1-up monitor can also be found, on the ledge to the right instead. (video)

Unused Sprites

Incorrectly Colored Bonus Stars

The spinning stars seen when activating a Star Post with 20 or more Rings do not display properly. Each Bonus Stage is meant to have its own uniquely colored stars to indicate which one can be entered, but only the largest star sprite features any difference. The two smaller star sprites were intended to be the same color as the large one, but they are instead seen with the same color as in Sonic the Hedgehog 3 regardless of which Bonus Stage is active. Even the large star sprite isn't completely safe from this as the bottom right corner of the sprite still uses a piece from Sonic 3. This was fixed in Sonic & Knuckles Collection.

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 Big Arm, 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. Sonic Origins would later use this jingle 27 years later, for the Launch Base Act 2 score tally (again, after defeating Big Arm).

DAC samples

A few DAC samples go unused.

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 is inside a wall.

ID 0D

ID 0D's Act 1 is merely a dummy slot used to load the stage palette for Angel Island Zone Act 1 in Sonic 3 when the intro cutscene (which uses a different palette) gets skipped, while Act 2 is the ending sequence for Sonic.

Gumball Machine Bonus Stage

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, since its data is also absent.

Carnival Night Zone (ID 03)

By entering Mushroom Hill Zone and then using Pro Action Replay code FFFE10:0300, you can actually view the remnants of Carnival Night Zone from Sonic 3, which contain the cycling palette and background scrolling data. This will cause some of the foreground graphics to become corrupted. Upon reaching the boss area, the game will softlock due to CNZ's boss code being removed from the ROM.

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 the player 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 and an invisible solid block, 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. If the Act's layout from the Sonic 3 Nov 3, 1993 Prototype is restored via hacking, the springs will line up perfectly with the top of the Capsules, matching the Zone's unused Data Select portrait from Sonic the Hedgehog 3.

Something similar happened with Casino Night Zone Act 2 in Sonic the Hedgehog 2, where two sets of rings were placed too high to reach and appeared to line up more with Act 1's layout.

Death Egg Zone Act 1

There are three rings placed in the floor under the first black antigravity ball. It's possible to collect these rings by getting a Lightning Shield, and backtracking here.

Palette Oddities

Lava Reef Zone Act 2

One of Lava Reef Zone Act 2's palette cycles, mainly used for the glowing crystals and pipes suffers from a programming error. Four palette indices are used for the cycle, but the third and fourth indices mistakenly use the same colors as the first and second, rendering half of the intended colors unused and making everything that utilizes the cycle look duller. The palette cycle is fixed in the remastered version created for Sonic Origins. To fix it yourself, use the Game Genie code ATXT-AAD2.

Lava Reef Zone Act 2 Boss

This glowing rock platform, seen on the Lavafall in the Lava Reef Zone Boss Act normally uses palette 03, but the top of the platform looks a bit odd. If it is set to use palette 02 (which Game Genie can do with the code AGTT-RAX6), it becomes clear that it was meant to match the look of the other platforms seen in the Act, as well as the dark red colored rocks. Sonic Origins compromises by having the top of the platform use palette 02, while the rocks use palette 03.

Sky Sanctuary Zone

The chain and link used to hold the checkered ball on the Green Hill Zone boss normally use palette 01. If they are set to use palette 00 (the same as the Egg Mobile), then the colors appear to mesh better. This palette would later be used in Sonic Origins. The Game Genie codes for this particular palette are PCXA-RJDE (for the link) and PCXA-RJDT (for the chain).

Incorrect Sprite Positioning

Unlike in Sonic 3, the first frame in Sonic's ending sprites is not centered correctly, leading to a jarring momentary shift as he transitions into his final pose. The following Pro Action Replay codes should fix the issue:

Sonic 3 Level Select Code

The Sonic 3 level select 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 it can only be inputted after the Sega logo but before the title screen appears, which is made harder via the ridiculous number of lag frames).

References