Sonic the Hedgehog 2 is a side-scrolling platform video game developed by Aspect and released by Sega for their Master System and Game Gear formats. The Master System version was released in Europe on October 25, 1992, and in Brazil around the same time. The Game Gear version was released in Europe on October 29, 1992, in North America on November 17 1992 and in Japan on November 21, 1992. Being released before the 16-bit version for the Mega Drive (Genesis), the 8-bit editions of Sonic the Hedgehog 2 represent the debut of character Miles "Tails" Prower, Sonic the Hedgehog's best friend who became a recurring character in the series.
(The storyline above comes from the game's instruction booklet. It is contradicted by an opening cinematic where Tails runs ahead of Sonic, and Sonic witnesses his kidnapping.)
So, Dr. Robotnik kidnaps Sonic's friend, Tails, and demands that Sonic brings him 6 Chaos Emeralds if he ever wants to see him again.
There are seven zones in total, each comprising three acts. In the final act, that level's boss is faced, but without any rings to collect. Rather than facing Robotnik himself (with the exception of the final stage and some involvement in the first boss), Sonic faces up against a bunch of robotic animals, such as a sumo pig and a circus sealion.
At the end of Acts 1 and 2 of each level, a panel is spun, with a reward given based on what it lands on:
Item boxes are largely the same as the first game (although the restart marker and shield devices have been removed), and as usual, Chaos Emeralds are scattered throughout the stages. Each is found in the second act in each of the first five zones. If the player collects these five and then destroys Mecha Sonic (called "Silver Sonic" in the English manual) in the sixth zone, the sixth is awarded and the player may access the final stage (Crystal Egg), in the third act of which Doctor Robotnik is faced in a climactic boss battle. Players able to complete the full task are rewarded with the game's "good ending"; for those who fail to collect all of the emeralds, play ends after Mecha Sonic's destruction with a more downbeat end sequence (in which Tails is assumed to be dead).
The music for the intro sequence is also different, the Game Gear version using the Scrambled Egg music for the scene showing Robotnik escaping with the captive Tails, with the tune that was played in this prelude in the Master System version instead employed on the title screen. The hand-held edition also features dark blue (instead of green) water in the second Act of the Aqua Lake Zone, and omits the game's only "High Speed" item box, which may be found in the Master System version of this stage.
In addition, the two versions have different themes for boss battles, as well as for their endings (the Master System uses a somewhat sad sounding tune for both the bad and good endings, whereas the Game Gear has a separate more upbeat tune for the good ending). This is strange since the Master System version actually contains both of the ending music in the game's code, but only one of them is used. A rather interesting note was that the music for Green Hills Zone was featured as the theme song for the Japanese and European versions of Sonic CD, and a negative remix of the tune is used for Mecha Green Hill Zone in Sonic Chaos.