Sonic Advance 2
Sonic returns for a second outing on the Game Boy Advance. Once again, Sonic must save the world from the evil Dr. Eggman. This time Sonic is joined by his friends Tails, Knuckles and Cream the Rabbit, the newest member of the Sonic team. Each of them has a number of unique moves that will let you reach certain areas in the levels. However, unlike Sonic Advance, you'll have to finish the game as Sonic to unlock the other characters. Chaos Emeralds and Special Rings are scattered throughout the levels. To collect the emeralds (which transform Sonic into Super Sonic for the final battle against Dr. Eggman), you'll have to find the Special Rings hidden in each level to unlock the bonus stage. Complete the bonus stage and the emerald will be yours. You'll also have the option to collect and level up Chaos and trade them into Sonic Adventure 2: Battle on GameCube using the GBA/GC Link cable.
Story
On an unspecified island, Dr. Eggman has again started kidnapping animals and turning them into robots so that he can build the Dr. Eggman empire. This time, however, he has also kidnapped Tails and Knuckles. When Sonic learns about the kidnapping of his friends, he rushes to rescue them. Along the way, Sonic rescues a young rabbit named Cream and her Chao friend Cheese from Eggman after defeating his EggHammerTankII. Cream joins Sonic on his adventure to find her missing mother Vanilla. Sonic soon saves Tails from Eggman as well, though Tails has no idea what Eggman is up to, and Tails joins Sonic on his mission. When Sonic finds Knuckles, the Echidna has been tricked by Eggman into fighting Sonic. After being defeated and rebuked by Sonic, Knuckles comes with him to get back at Eggman. The heroes eventually track Eggman to his Egg Utopia space station, which they destroy, and Cream finds Vanilla in the rubble, unharmed.