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.
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You get to the Middle of the maze and go against the dude with the wings.
go though all shadow doors then do to the door that leads to tabu
in the great maze, when you press + or start. there are many different bowser heads in different locations, they are the different bosses you've fought and all of the brawl characters on the subspace emissary. when done with that, you go to the place that looks like the jungle to the purple arrow and enter the big door to fight tabuu and once you defeat him, you win.
Toon link can be unlocked after beating tabuu at the great maze then going back to the forest level and when you get past the first mini brawl you will soon find a red door that never was there before go in and toon link will appear defeat him and he will join your team save and quit and you will unlock him.
You beat every character and boss in brawl, then go to the middle of the Great Maze which should look like subspace and all that; go to the middle and press up like you would for a normal door. You should find Tabuu there Warning- he is very hard to beat even on easy mode but you will find out how to beat him