Original: The game is a sequel to Sonic the Hedgehog 2 and follows on directly from the end of the game , in which Sonic defeated his enemy , Dr. Robotnik ; crash-landing on a floating island , Sonic encounters new character Knuckles the Echidna , and must once more retrieve the Chaos Emeralds while also working to stop Dr. Robotnik from relaunching his ship , the Death Egg .
Simplified: You can play as Sonic the Hedgehog or Miles ` Tails ' Prower , or both ( Tails follows Sonic and does what Sonic does if you play this way ) . Dr. Eggman is called Dr. Robotnik in the North America and Europe version of the game .