Its a puzzle that had hints about it throughout the game. You have to do the following combination: Down, Up, Down, Down, Left, Right, A, A, Down. Took me forever to figure it out. :P
You have to unlock the door first by finding all of the character trophies throughout the maze. Then you just have to find the right spot in front of the massive door and tell the character to move up.
First, go to the map. Select the upper left The Great Maze. Select your characters and go through the gold door. Head left and go down the ladder and break your way through the blocks and head through the door. Keep going left until you reach a door that has a purple arrow pointing at it. Go through it to reach the trophie room.
you have to beat Tabuu, get all the character's trophies, and get through it all.
I assume you're referring to the Great Maze. You must kill every character in the maze until they're all behind the door, and then you can go through. The characters are all in different coloured doors.
If you mean in The Subspace Emissary, then the final level is The Great Maze, but there are four of those. Beat all the bosses, and then, you will have to go through the huge door in the middle room of The Great Maze, and you get Sonic and fight Tabuu.
go though all shadow doors then do to the door that leads to tabu
I think you must defeat every shadow character and boss in The Great Maze.
After you defeat most characters/bosses in the great maze through the shadow doors you'll see demon faces on your map. The demon faces represent the characters/bosses you have to defeat to get to Tabuu. After all the demon faces are gone, go to the save portal on the top right of your map. Then go through the bottom left door then go all the way to the left until you see a purple arrow pointing at a door. Go through the door & you'll see Tabuu's door with no trophies. Go through Tabuu's door & you'll see Sonic & will be able to fight Tabuu. Defeat Tabuu to complete The Great Maze.
You get to the Middle of the maze and go against the dude with the wings.
mario
When in boss battle mode in single player: Fight till the end When in subspace emissary: you need to completely scan through the great maze and fight all the bosses and dark character forms, when you do, the great big door in the center-ish room of the maze will open up. Simply press up to enter.
just keep walkin through doors till u find 1