This page documents bugs/glitches that have been found in Sonic the Hedgehog 3, as well as specifying whether each bug was ever fixed in a subsequent version of the game (i.e. Sonic 3 & Knuckles or Sonic & Knuckles).
In Acts where the level wraps vertically, the player can duck, wait for the screen to scroll down, then immediately jump, causing the screen to mistake the player's position and make the screen scroll all the way around. During this time, the player can move through certain objects, including kill planes, allowing access to otherwise restricted areas.
There are numerous bugs in the way music is played and resumed.
If invincibility wears off during a boss, there is no change to the music.
This behaviour dates back to Sonic 1, and is still generally the right thing for normal invincibility: the player would have become invincible by collecting an invincibility monitor prior to the boss starting, which would mean the invincibility music was then replaced by the boss music, which should not change when it wears off.
However, it does not account for Super Sonic. If Super status is lost by running out of rings or being smashed by the final Launch Base boss (which may be considered a bug in itself), the invincibility music will continue to play. This also results in the invincibility music continuing throughout Launch Base's ending if the boss was defeated as Super Sonic.
There are also some cases where the boss flag is not set or cleared at the correct time. This is most noticable when defeating the midboss of Marble Garden Zone as Super Sonic: as the boss flag is never set during this boss, the Act 1 music will restart very briefly as the boss is defeated, due to Super Sonic's invincibility being cancelled. In Angel Island Zone Act 1, if you are invincible, and you go up to where you meet the Act 1 boss before it engulfs the Zone in flames, but don't trigger the cutscene, the invincibility song keeps playing even after the invincibility wears off. This is caused by the boss flag having been set too early. The only way to stop it is by meeting the boss and continuing with the level.
Sonic the Hedgehog 3's seamless act transitions are written in such a way that the physical level does not need to change over at the exact same point as the logical end of act. Angel Island Zone and Icecap Zone make use of this; the former's level transition occurs when the island burns, while the latter switches while running through the tunnel out of the cave into daylight.
If the player restarts at a checkpoint or after a special stage in these transitionary areas, the correct Act 1 title card will be shown, but Act 2's music will play. There is one checkpoint on each route in Icecap where this can occur, and one checkpoint and a special stage in Angel Island. Sonic 3 & Knuckles contains a special-case fix for the checkpoint only in Angel Island, but the bug still occurs in all other situations, including at the special stage a few pixels away.
While fighting any boss where water is present, if you stay underwater long enough to trigger the drowning countdown, and then jump out of the water, the music for Sonic 3 & Knuckles’ mid-boss fights is played instead of the correct track. This behaviour also seems to date back to Sonic 1, where resuming music after drowning was handled with a lookup table with a single special case for boss areas, rather than using the stored previous track as Sonic 3 does elsewhere. This bug is much less noticable in Sonic 3 & Knuckles, as the Sonic & Knuckles midboss music happens to be the correct track to resume during the Hydrocity midboss fight, which is by far the more likely of the two water bosses to induce drowning.
Note that Super Sonic can be involved in other bugs that are specific to certain levels, which are described in the relevant sections below; this section is only for those that span the entire game.
If playing as Sonic or Sonic and Tails, becoming Super Sonic and rolling will cause the player to slow down.
Super Sonic can perform the bubble shield bounce. This is incorrect because Super/Hyper characters are not supposed to, and in all other circumstances do not, gain shields’ double-jump powers (although they do collect and ‘store’ them and will gain the graphics and power as normal upon exiting their Super/Hyper state).
Cheating via the combined level select/sound test screen enables various other glitches.
Various glitches are caused by passing a checkpoint in any zone and then picking another zone via level select. It causes the title cards to be wrong (referencing the level in which the checkpoint was hit) and Sonic/Tails get spawned in very odd places within the level, including walls, as the checkpoint coordinates do not match a sensible position in the new level. Also, objects sometimes don't load or they don't work properly.
Selecting Angel Island Zone Act 1 in this matter is particularly problematic, normally causing the game to freeze. This is because hitting a checkpoint in a zone without water will cause the checkpoint water level to be set to 00. This will result in water filling the entirety of Angel Island act 1 when entered, a scenario which crashes the game.
When visiting the Gumball Bonus Stage by selecting the sixth "2P VS" the level select, its title card will often appear garbled, as the wrong artwork is loaded for its lettering - most often Angel Island's, resulting in something that looks a bit like "DOILUS STAGE".
By using the level select, it is possible to see Knuckles with strange palettes underwater in various places.
In Sonic the Hedgehog 3, the music for Flying Battery Zone is present in the sound test, since the Zone was originally intended to exist in this game between Carnival Night Zone and IceCap Zone. In this version, the echo track of both acts' music will go off sync after the first loop, and slowly gain more and more delay behind the lead melody.
At the end of Angel Island Zone Act 2, playing as Sonic and Tails, you are chased by Robotnik's "Flying Fortress", which drops bombs that are easily avoided simply by running at full speed. Tails however will catch up with Sonic and then slow down to avoid overtaking Sonic, and will therefore be caught by the bombs. This occurs in Sonic 3 alone and Sonic 3 & Knuckles, and Tails is repeatedly hit by bombs; however, in the former, after being hit by a bomb Tails will remain running at the very far left of the screen.
When travelling around Hydrocity Zone Acts 1 or 2, after rolling at speed up a 90 degree ramp transfer from floor to wall, the player character will sometime glitch inside the wall. It seems to happen more often if the character is rolling rather than running, and if the player is holding "down" on the controller during the roll.
In the section where you go through a loop that leads to a vertical corkscrew that darts underwater, and is followed by a small tunnel and then a thick blue floor that curves up and then back down, Tails can swim through the blue floor in this area if he jumps as soon as he exits the tunnel and then starts swimming at a 45 degree angle to the hill in the floor. Under the floor is nothing but the eventual bottom of the level. Incidentally spikes were placed under other supposedly inaccessible places of the level, just not here.
Hydrocity's midboss plays the music normally associated with Act 2 bosses. This could be considered a design choice, but is likely an oversight, given that the normal midboss track is reinstated in Sonic 3 & Knuckles.
After being swept through the tunnel into the cavern to face Robotnik in Hydrocity Zone Act 2, it is possible to skip the boss battle by quickly running through the area to the right, where the animal capsule can be found and activated. The end of level music will play, and the points will be added up. However, the bomb drop and blast sounds can still be heard from the boss, and the water spout will not appear to take Sonic and Tails (or Sonic and Tails playing solo) to Marble Garden Zone. Also, the character name in the score tally will sometimes glitch. But all is not lost: if the console is reset and the player re-enters the save-select screen, their saved game will have been updated to Marble Garden Zone and will allow them to progress as normal.
While fighting the Hydrocity Boss, if you allow Super Sonic to be drawn to the water plume, Super Sonic will lose the custom sprites and will appear as regular Sonic (spikes pointing down instead of up) though the yellow color is retained. His rings will also no longer count down. Furthermore, once this has happened, defeating the boss will result in Sonic retaining the Super Sonic yellow color even after bursting the egg capsule open. The score tally will also appear with Sonic's name in yellow instead of blue. Here is the glitch in action.
It is possible to defeat the mid-boss by using 2 player Tails before it has been activated properly. By stopping Sonic before the screen has been locked for the mid-boss fight, and killing the mid-boss using Tails, the act 2 loading sequence will be out of position and crash the game once the end-of-act sign has landed.
Accessing this boss as Knuckles (only accessed by using cheats or glitches) in Sonic 3 & Knuckles will randomly cause the same issue. Another effect that may be related is sometimes you cannot move Tails up and down; that is most likely due to Tails spawning too early, so when EggRobo digs into the ground, stay on the ground and wait for Tails.
If Sonic, playing alone, reaches the end of Carnival Night Zone Act 1 without dying or entering a Special or Bonus Stage since the start of the zone, Tails will be heard and then seen suddenly dying after the mini-boss is defeated. After the sign falls and Act 2 begins, Tails will reappear and fall into the stage, but will be unable to move, and must be left behind. Should Sonic manage to also then reach the end of Act 2 under the same conditions, Tails will be seen dying again after defeating Eggman, and will spawn again on the screen after the "Act 2 completed" messages complete. When moving to enter the cannon, Tails will be crushed against the ledge as the screen is forced to the right.
This occurs because Tails is not unloaded after being spawned for the start of the zone in which he delivers Sonic from the end of the previous zone (Marble Garden). Restarting from a starpost or giant ring will recreate the level objects, and Tails is not respawned.
It is possible for Graviton Mobile to drop the "ball" into the shaft that was used to get up to the boss fight. The shaft is just to the left of the boss fight area, and the ball is able to reach it since is not affected by the screen lock. The top of the shaft is blocked by an object to prevent the player falling back through, but the ball is not programmed to interact with this object. This uses debug to show what happens.
In Act 1, by using the vertical wrap glitch, Super Sonic can gain access to Knuckles' area. While in this area, there are icicle spikes that harm Super Sonic, thus the player loses all of their rings and Super Sonic transforms back into Sonic.
In Act 1, Tails will lose a life when going down the first slide past the first star post in the initial run of the act. This can be avoided if you can manage to re-enter the act, such as returning from a Bonus Stage or Special Stage (a giant ring can be found just above said slide), or after losing a life and respawning from the checkpoint. After returning in one of these manners, Tails can go down the slide without issue; however, dying and returning to the beginning of the act, and not from the checkpoint, will not fix the issue.
The bug is caused by an oversight in the code. The vertical looping flag on the initial run is set during Sonic's snowboard sequence at the beginning of the act. Since this sequence is not triggered for Tails, the flag is not set when entering the zone for the first time. When Tails goes down the slide, which happens to be at the bottom of the level, the lack of the looping flag treats this as Tails falling into a bottomless pit.
Amusingly, the English manual makes an oblique reference to this bug, while trying to avoid identifying it as such: "In the IceCap Zone and throughout the game, avoid having Tails get stuck in passageways or get caught in traps. Have Tails activate Starposts or enter into a Special Stage as quickly as possible."
When playing as Super Sonic in Launch Base Zone Act 1, if the player holds left whilst Super Sonic is inside a "spinning elevator", he will glitch outside the elevator in the "push" pose before the doors of the elevator open.
In Launch Base Zone Act 2, when the final boss (Big Arm) slams Super Sonic against the ground, he can still lose rings.
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