Sonic the Hedgehog 2

South Island has been peaceful since Dr. Robotnik's defeat. Sonic, bored, decides to go on a journey in search of other adventures. Upon his return, he is shocked to find the island nearly abandoned. The only clue as to where all his friends might have disappeared to was Tails being chased by Dr. Robotnik. Sonic chases after him, but he is too late to save Tails. Sonic finds out that he's been kidnapped by Dr. Robotnik and is being held in a place called Crystal Egg. The price for Tails' safe return are the 6 Chaos Emeralds, to be delivered to 6 new boss robots. Thus, Sonic goes on a quest to find the Chaos Emeralds and rescue Tails.