Instructions
Complete all of team stories: Sonic, Dark, Rose and Chaotix. Try to collect all of the chaos emeralds the first time you play through the team stories, but if you miss some you can go back to get them later.
Make sure to obtain all seven of the chaos emeralds that can be found in each team story. Once you have all of the emeralds and team stories complete you will have unlocked the final stage. Go to the main story screen and press your right button until you get to the screen with Metal Sonic on it. Click your "A" button to enter the final stage.
Start the first battle as Team Rose and play as the other teams during the following battles. Each team will have to fight a boss that is similar to the last level bosses of each team's story. Press the "A" button to get through the story and begin the battle.
Defeat the Metal Madness boss by using the advantages and strengths of each character on each team. Look at the color of the plate near Metal Madness's tail and use characters that are the opposite color to avoid damage.
Play as Super Sonic's team for the final boss and last possible level of the game after you've defeated Metal Madness. You will have unlocked Super Sonic and the Super Sonic team as a playable character in the game.