Debug Mode, also referenced as Debug Menu, is a program used by the developers of a videogame or other software for "debugging" purposes; locating erroneous programming, that can be found by the game's testing groups and which will be corrected/fixed after being detected before the game's final release. In most videogames, debugging menus are meant to be accessed only by the game developers themselves and are almost always made out of reach for players, unless using cheat codes to activate them.
In the first installments of Sonic the Hedgehog games for the Sega Genesis, Debug Mode can be found by using a cheat code. In Sonic Mania, it is instead activated as a feature from a "No Save" game. Once the player has then activated Debug Mode in-game, the player is able to break the rules of the game in many ways possible.
In earlier Sonic the Hedgehog games, after activating a cheat code, the player may notice "Score" (even sometimes "Time") on the HUD having a different look, as the debug coordinates (in hexadecimal format) of the playable character and screen replaces the score. The player is able to play normally until he/she presses , which activates Debug Mode in-game screen. The playable character can turn into different objects. In this state, the player is able to move wherever he/she wants.
When in this state, the player is able to press again to deactivate Debug Mode. With , the player can cycle through list of placeable objects or press both and to cycle through the list in the other way. With , the player is able to select the objects of the Zone he is in and add them to its place. The objects that are not normally seen in the game can reflect to possible concepts for the game that were planned or supposed to be added during the game's development but got scraped/unused later on. Not every unused content of the game is featured in Debug Mode and many of them are not programmed to work at all. If the player adds too many objects at once, it is known to cause lagging and other technical problems within the game. Due to the program tool not originally meant for usage by players, the game may erase the saved data in cartridges, CDs or any other formats if the game glitches or crashes by using the Debug Mode.
In Sonic the Hedgehog 3 & Knuckles for the Mega Drive, if the player press both and , the character will scroll through the available sprites in the game. It is not known if it is possible to perform this in other games.
Some games have also other features that are seen in Debug Mode. In Sonic the Hedgehog 3& Knuckles, the player is also able to change gravity from normal to upside-down by pressing , in which the playable character, enemies and other objects start raising upwards until the bottomless pit or the roof comes across.
The earlier installments in the series are known to have a specific cheat code to activate them, while after Sonic & Knuckles, the only way is to get cheat codes that activate Debug Menus in video games. You can find them by using identifiable cheat cartridges, that can read codes such as GameShark. However, the following list contains available ways to activate Debug Mode in certain Sonic games without using any cheat cartridges:
Sega Genesis: In the title screen press ↑ ↓ ← →, the ring chime can be heard and hold then down and press start button to begin the game with Debug Mode. In revisions of the game, the code is inexplicably changed if played on a Japanese console.
2013 re-release: At the Level Select Sound Test, play the following tunes in order: 01, 09, 09, 01, 00, 06, 02, 03. Then after selecting a Stage to play, the player then has to tap the HUD on the upper-left corner of the screen to activate Debug Mode. Once there, the player can cycle through the placable objects by tapping the minus or plus buttons, move around with the directional pad and place them by tapping the jump button. To exit out of Debug Mode, the player must tap the HUD again.
1992 original: The player has to activate and have then entered the Level Select screen. There, play the following music in order: 01, 09, 09, 02, 01, 01, 02, 04 at the new Sound Test section. Then hold down and select one of zones of the game and press start.
2013 re-release: After accessing the Level Select, the player has to play the same music tracks in the same order as the original release in the Sound Test. The controls remain the same from the 2013 re-release of the original Sonic the Hedgehog and in addition, the player can return to the Level Select anytime while in Debug Mode by tapping the top right corner of the screen where the pause button would be.
Sonic the Hedgehog 3: The player has to enter the Level Select code and head to the Level Select screen. Here the player has to hold down, select one of Zones/Acts in the game and then press start button.
Sonic the Hedgehog 3 & Knuckles: The player has to activate Level Select code and then head to the Mushroom Hill Zone (Act 1 is the fastest and recommended choice). Here the player has to jump one of pump elevators and then press ←←←→→→↑↑↑. The ring chime can be heard, then pause the game and press to head back to the title screen and then head to 1 Player or Level Select. There, select one of zones of the game, hold down and then press start. A glitch with the S monitors causes Sonic 3 and Sonic & Knuckles to internally disconnect, yet keeping most of the variables intact, allowing for Debug Mode in Sonic & Knuckles alone, as well as showing Marble Garden Zone demo, either as a Passover or leftover data.
Knuckles the Echidna in Sonic the Hedgehog 2: The player has to activate the Level Select code and head to the Level Select screen. Here, play songs 01, 09, 09, 04, 01, 00, 01, 08 in order at Sound Test part and the Ring chime can be then heard. Then press down, select one of Zones/Acts in the game and press start.
The 8-bit version of Sonic Spinball features hidden secrets, that are sort of related to be Debug Mode of the game. On the left edge of each stage is known to have a hidden small chamber, that contains three Item Boxes. Each of them contains 1-Up, Continues, and a special variant with 見る on it (Japanese characters for "look"). Breaking this Item Box will give a hint for a secret code. The codes are as follows, to be played in order at the Sound Test of the game in options menu. Putting code right makes the screen do small shake and the code has then activated. Following codes and their purposes:
By playing 0, 8, 3, 1, 7, 1 in Sound Test gives the player full codes instead of hints when the player hits the Item Box with 見る kanji on it in each stage of the game.
By playing 0, 2, 1, 1, 6, 6 in Sound Test will make Sonic's sprites in general 3 times larger. Despite the large sprites, the game plays normally.
By playing 0, 9, 0, 1, 6, 8 in Sound Test makes the player move everywhere in the stage. The player has to pause the game and then press 2 button, thus being able to move around with the D-pad.
By playing 0, 2, 1, 5, 6, 6 in Sound Test will give option to skip to the next stage. This is able by pausing the game, pressing down on D-pad to skip the stage to the another one.
By playing 0, 4, 2, 5, 5, 7 in Sound Test will make BGM in the stage extremely fast.
In Sonic Mania, and its expansion Sonic Mania Plus, players can unlock Debug Mode by obtaining at least sixteen Medallions from the Bonus Stage. This will unlock Debug Mode as a feature that can be toggled on or off in No Saves mode.
Originally, there was a cheat code for unlocking Debug Mode. First, the player had to hold // and //, then press any other button to access a special Level Select screen in the style of Sonic the Hedgehog 2. After selecting a level, the player then had to press // to access Debug Mode in-game. However, this cheat code was patched out in ver. 1.03.
Depending on the game, numbers in Sound Test that are set on to activate Debug Mode are noticed to format specific dates, which can also happen when the player tries to activate Level Select code as well.
Playing songs to activate the Debug Mode in Sonic the Hedgehog 2 can format date November 24, 1992, the game's release date in the United States.
In the 2013 re-release of Sonic the Hedgehog (1991), playing songs at Sound Test for activating Debug Mode can also format June 23, 1991. This is the release date of the original Sega Genesis version of the game in United States and Europe.
The cancelled Sega Saturn game Sonic X-treme also has a debug mode in the 714 build. It is activated by pressing Start and then . Unlike other games, it's available from the start and it cannot be exited from. The only object the player can place is a Ring, by pressing Start and then .
Beta builds from certain games (particularly Sonic the Hedgehog 2), such as the Simon Wai and Nick Arcade prototypes, also featured Debug Mode, albeit in a rather unfinished state and still under development, often only allowing the player to place Rings and Super Ring monitors.