Story: The friends of Sonic and Tails are disappearing and strange robots are appearing. Sonic heads off to find Robotnik, who has not yet found the Chaos Emeralds. The Chaos Emeralds would give Robotnik the power to conquer the entire world. It's up to Sonic to find the Chaos Emeralds and stop Robotnik.

Levels: There are 11 stages (zones) in Sonic the Hedgehog 2:

Emerald Hill Zone (Act 1 and 2)
Chemical Plant Zone (Act 1 and 2)
Aquatic Ruin Zone (Act 1 and 2)
Casino Night Zone (Act 1 and 2)
Hill Top Zone (Act 1 and 2)
Mystic Cave Zone (Act 1 and 2)
Oil Ocean Zone (Act 1 and 2)
Metropolis Zone (Act 1, 2 and 3)
Sky Chase Zone
Wing Fortress Zone
Death Egg Zone

At the end of each stage (with the exception of Sky Chase Zone) is a battle with one of Robotnik's creations.

Chaos Emeralds: Sonic can collect the seven Chaos Emeralds (there were six in the first Sonic the Hedgehog game) by collecting 50 rings in a stage and then touching a star post. A star circle will appear, and after Sonic jumps inside he will begin playing a special stage. Sonic must collect the number of rings specified in the special stage to reach the Chaos Emerald. When Sonic collects all seven Chaos Emeralds, he can become Super Sonic by collecting 50 rings in a stage. Super Sonic is invincible as long as he has rings. The number of rings decreases at the rate of one per second, and when the ring counter reaches zero Sonic will return to normal.

The special stage is different than in Sonic the Hedgehog. Instead of a 360 degree rotating maze, Sonic now runs through a pipe collecting rings. If Sonic and Tails enter the special stage together, they must collect more rings than if the game was played with Sonic alone or Tails alone.

Note: Although Tails can collect all seven Chaos Emeralds, he cannot turn into Super Tails. Only Sonic can become super.

Miscellaneous: The controls for the game are the same as the first game: the directional pad moves Sonic and the buttons (A, B, and C) can be used to make him jump. Sonic has learned a new technique called a super dash attack (later called a spin dash attack). To perform the super dash attack, hold down on the d-pad, press one of the buttons to generate speed, and then let go. You can press a button repeatedly to generate more speed.

When a game starts, the default is to play as Sonic and Tails follows Sonic. Under the Options screen (accessed through the Title Screen), "Sonic Alone" and "Tails Alone" can be selected. By selecting Tails Alone, Tails can collect Chaos Emeralds and play the stages. However, Tails cannot turn super like Sonic and cannot fly.

Sonic the Hedgehog 2 also has the first two-player versus mode in a Sonic game. Sonic and Tails can race against each other in three stages (Emerald Hill, Casino Night, and Mystic Cave) and collect rings in special stages. The player that wins the most stages is the overall winner. Stages are scored based on time, rings, finishing score, total points, and item boxes. In the event of a tie, the players must compete in a special stage to determine the winner.