Debug Mode

Debug Mode, also referenced as Debug Menu, is a program from the development of a video game or other software. In game developing, Debug Mode is only meant to be used by game developers themselves for debugging - 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 almost all video games, debugging menus are made to be impossible to get access for normal gamers, unless using cheat codes to activate them.

In the first installments of Sonic the Hedgehog games for Sega Genesis/Mega Drive, Debug Mode can be found by using a cheat code. 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, including free movement.

Overview
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 whereever he/she wants.

In this point, the player is able to press again to return 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 object of the zone and add them to its place. The objects that are not normally seen in the game can reflect to the player possible concepts for the game, that were planned or supposed to being added during the game's development but could possibly get scraped or become unused. Not every unused content of the game is featured in Debug Mode and many of them aren't programmed to work at all. If the player adds too much placements in one place, it is known to cause lagging and other technical problems within the game. Due to the program tool not originally meant for usage by normal players in first place, 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.

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 backwards by pressing, in which the playable character, enemies and other objects start raising upwards until the bottomless pit or the roof comes across.

Known cheat codes to activate Debug Mode
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:

Sonic the Hedgehog (Genesis)

 * 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 upper-left corner of the screen to activate Debug Mode.

Sonic the Hedgehog 2 (Genesis)

 * 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.

Sonic the Hedgehog CD

 * Sega Mega CD: The player has to insert Sound Test code in the title screen. Then player adjust FM#40, PCM#12, DA#11 to their own places and then press the start button. The player will get then extra picture featuring Tails with words See You Next Game" from character's designer Yasushi Yamaguchi. The game then progresses to the title screen.
 * 1996 PC Release: The player has to insert Sound Test code in the title screen. Then the player must adjust PCM#12, DA#11 and then press SPACE in the keyboard.

Sonic the Hedgehog 3 & Knuckles

 * 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 in the game and then press start button.
 * Sonic the Hedgehog 3 & Knuckles: The player has to activate Level Select code and 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 there to the Level Select screen. There, select one of zones of the game, hold  down and then press start. A glitch with the S monitors also allows for a glitch causing Sonic 3 and Sonic and Knuckles to internally disconnect, yet keeping most of the variables intact, allowing for S&K alone debug mode, as well as showing Marble Garden Zone demo, either as a Passover or leftover data.
 * Knuckles 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 in the game and press start.

Sonic Spinball (Game Gear/Master System)
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"). Braking 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.

Trivia

 * 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 US release date.
 * This is similarly repeated in Knuckles in Sonic the Hedgehog 2, where putting Debug Mode code can format date October 18, 1994, when Sonic & Knuckles was released in US and Japan.
 * Years later in 2013 the re-release of original Sonic the Hedgehog, 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 US and Europe.