In Sonic the Hedgehog 2, the main goal is to complete each level as quickly as possible, and with as many Rings as possible. The game consists of six Zones, with the possibility of a seventh. Each Zone consists of three levels called Acts. Hidden very securely in the second Act of the first five Zones, and the third Act of the Scrambled Egg Zone, are objects known as Chaos Emeralds. Sonic must find all six Chaos Emeralds, and clear the first six Zones, in order to gain access to Dr. Robotnik's hideout in the Crystal Egg Zone, where his friend Tails is being held hostage.
Rings
Rings are round, golden objects, hundreds of which are scattered throughout each Act. Their main purpose is to 'protect' Sonic; if he is hit by an enemy while carrying Rings, he will lose all his Rings instead of a life. He can recollect a small number of Rings lost, should this happen. Sonic can only lose a life if he falls into an abyss, or if he is hit while not carrying Rings. Collecting one hundred Rings grants you an extra life.
Zones
Zones are groups of levels (Acts) with a similar theme and level structure. There are seven Zones in total. Some Zones have special items exclusive to that Zone, that are important to the navigation of its Acts. There are three Acts in each Zone. The second Act of the first five Zones, and the third Act of the sixth Zone, contain a Chaos Emerald in a secret location, which must be found in order to fully complete the game.
At the end of the third Act of each Zone, Sonic must defeat the Zone's Boss Mecha in order to progress to the next Zone. The third Act never contains any Rings, meaning that you must avoid all attacks from the Boss Mecha, since one hit will result in your defeat.
End-of-level panels
At the end of Acts One and Two of each Zone, a yellow panel must be spun to complete the Act. The icon shown on the reverse of the panel, one of a possible four, may or may not reward you for clearing the Act. The four possibilities are:
- Robotnik: The most common of the four. This carries no reward.
- Ring: This adds ten Rings to your total Ring count.
- Sonic: This grants you an extra life.
- Tails: The rarest panel, this rewards you with a Continue.
The Chaos Emeralds
If you search Act Two of the first five Zones very thoroughly, you may find one of the six Chaos Emeralds. These magical jewels are the most important objects in the game. They are desired by Dr. Robotnik, who has kidnapped Tails, demanding the six Emeralds as ransom, in order to acquire them. Sonic must find all six Chaos Emeralds, so that he can gain entry to the Crystal Egg Zone, the final Zone where Robotnik holds Tails hostage. If Sonic does not have all five Chaos Emeralds before entering the sixth Zone, he will be unable to find the final Chaos Emerald, thus altering the game's ending.
Check the spoilers in Sonic the Hedgehog 2 (8-bit)/Scrambled Egg Zone#Act Three to see how the game's ending is altered.
Differences between the Master System and Game Gear versions
- The Game Gear version has a lower resolution, making many parts of the game more difficult. This is most apparent when fighting the Boss Mecha of the first Zone, as it is harder to notice incoming bouncing balls.
- Different music is used for the title screen, Boss battles and ending scenes in each game.
- The Boss battle of the fourth Zone takes place on a steeper hill in the Game Gear version.
- The Speed Shoes power-up is only in the Master System Version, It is unused in the Game Gear Version.