Sonic returns for a second outing on the Game Boy Advance. Once again, Sonic is called upon to save the world from the evil Dr. Eggman. On this occasion, Sonic is joined by friends Tails, Knuckles and Cream the Rabbit, the latest addition to the Sonic team. Each comes with a set of unique moves, allowing you to reach certain areas through-out the levels. However, unlike Sonic Advance, you must complete the game as Sonic to unlock the other characters. Chaos Emeralds and Special Rings litter the stages. To collect the emeralds (transforming Sonic into Super Sonic for the final battle with Dr. Eggman), you must find the special rings hidden in each stage to unlock the bonus stage. Complete the bonus stage and the emerald is yours. You'll also get the chance to collect and raise chaos, and trade them over to Sonic Adventure 2: Battle on GameCube, through the use of the GBA/GC link cable.