Sonic the Hedgehog 4: Episode I is a 2010 platform game developed by Dimps with assistance from Sonic Team and published by Sega. It is a sequel to Sonic & Knuckles (1994) following Sonic as he sets out to stop a returning Doctor Eggman. Like the Sonic the Hedgehog games released for the Sega Genesis Episode I features side-scrolling gameplay with movement restricted to a 2D plane. The player races through levels collecting rings while rolling into a ball to attack enemies. The game also features special stages in which the player collects Chaos Emeralds and online leaderboards comparing level completion times and high scores.