Sonic the Hedgehog 2 is a side-scrolling platform game.[1] It features a story similar to the first Sonic the Hedgehog's (1991):[2] Doctor Robotnik, a mad scientist, seeks the Chaos Emeralds to power his space station, the Death Egg,[3] and traps the animal inhabitants of West Island in aggressive robots.[4] As Sonic the Hedgehog, the player embarks on a journey to collect the Chaos Emeralds and stop Robotnik.[4] The player character can run, jump, crouch, and attack by curling into a ball.[5] Sonic 2 introduces the spin dash, which allows the player to curl while stationary for a speed boost,[1] and Miles "Tails" Prower, a fox with two tails who acts as Sonic's sidekick. By default, the single-player controls both Sonic and Tails simultaneously; a second player can join in at any time and control Tails separately.[3] The player can also choose to play as Sonic or Tails individually.[1][6]
The game takes place across 10 zones with 23 levels ("acts").[7] The acts are larger than the first game's,[8] and the player navigates them at high speeds while jumping between platforms, defeating robot enemies, and avoiding obstacles.[9] Springs, slopes, bottomless pits, and vertical loops populate acts, as do hazards like water and spikes. The player passes checkpoints to save progress. The last act of each zone ends with a boss battle against Robotnik.[10] The player collects rings as a form of health: if they have at least one ring when they collide with an enemy or obstacle, they will survive, but their rings will scatter and blink before disappearing.[2] The player starts with three lives, which they lose if they are hit without a ring, fall down a pit, get crushed, drown, or reach the 10-minute time limit; they receive a game over if they run out.[11] Power-ups like shields and invincibility provide additional layers of protection, and lives are replenished by collecting 100 rings or a 1-up.[12]If the player passes a checkpoint with 50 or more rings, they can warp to a special stage for an opportunity to collect one of the seven Chaos Emeralds.[3] The player runs through a half-pipe course, collecting rings and dodging bombs. A set amount of rings must be collected to obtain the emerald.[2][13] If the player collides with a bomb, they lose ten rings and are immobilized momentarily. The stages rise in difficulty and the player cannot enter any stage without passing the previous one. After finishing, the player is transported back to the star post they used to enter, with their ring count reset.[14] When all the Chaos Emeralds have been collected, Sonic can transform into Super Sonic by collecting 50 rings. Super Sonic is nearly invincible, runs faster, and jumps farther, but loses one ring per second and reverts to normal when his rings are depleted.[3]Sonic 2 introduces a multiplayer game mode where two players compete against each other in a split-screen race across three levels.[3][9] After one player finishes a level, the other player must finish within a minute. Players are ranked in five areas (score, time, rings held at the end of the level, total rings collected, and the number of item boxes broken). The player who excels in the most categories wins.[15] Players can also compete to obtain the most rings in the special stages.[16]