Instructions
Check the map for the Great Maze that is found on your subscreen. Push the pause button and go to the FAQs section to find the map. On the map, the green dots represent doors and the white lines show where they lead.
Look for the dots on the map without white lines. These represent doors with dark characters behind them; head for that location on the map and you'll find a door surrounded in black smoke. Locate all of these doors in the Maze and defeat the dark characters behind them.
Travel the entire maze in a circle, beating each character you find. Locate the purple room in the center of the maze with the trophies. Once you have done that, clones of the boss monsters you beat earlier in the game will appear in the maze; they'll be shown on the map with Bowser heads marking their positions.
Defeat all the dark characters and boss monsters and return to the trophy room in the Maze's center. The purple door in the room is now open. Behind it, you will find the last boss, Tabuu. Defeat him to finish the Great Maze and conquer the Subspace Emissary.