Sonic Crackers

Sonic Crackers, also known by the name in the ROM header, Sonic Studium, is an early Sonic the Hedgehog prototype game for the Sega Mega Drive/Genesis. It is believed to have been an engine test, containing essentially multiple different game engines, swapped out in realtime using code written into RAM.

Gameplay
The game has Sonic and Tails joined together by a band of rings. This would later become the idea for Knuckles' Chaotix for the Sega 32X.

The ROM has two "adventure" levels, one of which appears multiple times with a different palette each time, and two "field" levels. One is highly reminiscent of the Techno Tower Zone level in Knuckles' Chaotix, the objective being to make it to the top of the screen; if this is done or three full minutes elapses on the clock, the Sonic 1 "game over" music plays and the player is brought to the first field level, featuring a clouded background and a waterfall.

The "field" levels are only half-complete; there is no collision set, and Sonic can walk anywhere on the field with impunity. If the player pauses and hits a button, the game goes to a carnival-like level reminiscent of Chaotix' Speed Slider Zone that goes around in an infinite loop. After one minute has elapsed, the circus level ends and another "field" level begins. After the player pauses and hits another button, he or she is brought back to the Techno Tower Zone level with a different palette, four in all.

The Chaotix Connection
Though Sonic and Tails are missing from the final version of Knuckles' Chaotix, some believe that evidence still exists that they were once part of the game, as shown in Sonic Crackers. A short summary of some of the evidence includes:

Other now-discredited theories suggested Sonic Crackers to be:
 * The fact that Heavy & Bomb have yellow and blue colored statues, respectively. These could have been the reserved statues for Sonic & Tails or may hint that Sonic and Tails could have been captured and turned into Heavy and Bomb.
 * The presence of Sonic and Tails in the Sonic Crackers alpha version in what appears to be Techno Tower. This could indicate they were simply removed in an early phase of development. Alternatively, Sonic and Tails could have served as generic placeholders for characters not yet designed. Additionally, an alpha version of what could be Speed Slider can be accessed.
 * The Mighty the Armadillo sprites in Knuckles Chaotix are very similar to those of Sonic in the other 16-bit games. Some of Mighty's animations also match new animations given to Sonic in Crackers.
 * The Level Select cheat code in Knuckles' Chaotix allows you to manually select what character you want to play as. In the lineup, Mighty the Armadillo is listed in the first slot, typically where you would find Sonic in the Sega Genesis Sonic games. Listed second, is a character named **********. This character can be selected and played in-game. It uses a scrambled version of Knuckles' tileset on Mighty's palette, and behaves like Mighty. This character has been dubbed "Wechnia". Some speculate that this is where Tails once was, and rather than deleting the slot completely when he was removed, the programmers simply changed the name and pointers.
 * There are two copies each of Heavy & Bomb in the Combi-Catcher (as opposed to one copy each of all the other characters). Some fans believe that the extra spaces would have been reserved for Sonic & Tails, but it's also possible that the duplicates were designed from the start to increase the player's chance of a getting a 'lesser' character.
 * An ending screen showing artwork of Sonic & Tails in front of the Chaotix team when the game is completed with all Chaos Rings.
 * The presence of Metal Sonic in a game where Sonic himself is largely absent.
 * The presence of Amy Rose, hidden in the sound test.
 * Sonic Crackers stage select referring to levels as 'attractions' instead of 'zones'.
 * Knuckles' Chaotix music tracks, "Walkin'", "Hyper-Hyper", "Evening Star", and "Moonrise", as well as a version of "Electoria" based on the four previously mentioned tracks, can be heard in Sonic Crackers, as well as the Game Over theme from the first two Sonic games.
 * The "character switch" item box in Knuckles' Chaotix has has two arrows, one blue, and one orange, the respective colors of Sonic and Tails


 * Sonic the Hedgehog 4 - Critics point to the use of Sonic 1 sprites rather than Sonic 3 sprites, saying that this made it rather unlikely that Crackers was built on the Sonic 3 engine as the previous two sequels had been.
 * A hoax, either by Sega or homebrew - proponents pointed to the "19940401" on the title screen, citing this as April 1, 1994 . This theory has been discarded because of the large amount of work that this would require, and also because of numerous leftover pieces of art which indicate the game was a work in development, rather than a deliberately unfinished complete piece.