Sonic Blast (Game Gear)
This game has unused code.
This game has a prototype article
Press Up, Up, Up, Down, Down, Down, 1, 2, 1, 2, Start at the title screen.
A build date is present at 0xC0:
GG SONIC 96 Ver E3 ROM 1996/05/01 @SEGA /Aspect Co.,Ltd
This predates the earliest available prototype (dated May 31, 1996), which also contains this text.
The real build date is very likely September 10, 1996, as a build labeled "Prototype 910" is bit-for-bit identical to the final ROM.
All of the 8-bit Sonic titles developed by Aspect contain a generic error handler routine at ROM 70. While the other games' routines consist of some variation on "print an error message and reset", the Sonic Blast handler simply freezes the game by going into an infinite loop. Since the game doesn't call this routine and the Z80 has no hardware error trapping, this code will only execute in the extremely unlikely event that a bug coincidentally causes the game to jump directly into it.
Present in the graphics for Sonic is this unused animation of the Strike Dash ability, which was in Sonic Chaos and Sonic Triple Trouble. All that remains of this move is this animation, which is stored with a vastly different object palette than used in the final game. (The above sprite animation was given a proper palette for visual clarity.)
The music used for the opening cutscene lasts 31 seconds, but only the first 6 seconds are heard in-game.
The game was known as G Sonic in Japan, so the title screen reflects this. The title screen animation is also different.