is a 1994 platform video game developed by Sonic Team and published by Sega for the Sega Genesis/Mega Drive. Released on October 18, 1994, it was the fourth installment in the main Sonic the Hedgehog series. The game is a direct sequel to Sonic the Hedgehog 3, and follows both Sonic the Hedgehog and Knuckles the Echidna in their respective quests to save Angel Island; Sonic tries to prevent Dr. Robotnik from re-launching his orbital weapon, the Death Egg, while Knuckles scuffles with Robotnik's minion, EggRobo.