Ok i have finished the game on the PC and i'll tell you how to finish againt chaos when he has 7 emeralds. Ok you have to complete the game with every character so that when it says character select it has 100% next to it. If you have done this then there should be an extra character, click on this and you get to play against perfect chaos (chaos with all emeralds) as super sonic
I really wanna chocolate muffin now.