You will have to speak with Toad to unlock a quest in which you catch rabbits. Once you have completed this quest, you can use the white door for Super Mario 64 DS.
It's at the top of the flight of stairs on the second floor.
You enter the castle, go up the stairs and to the right, into the door with the 1 on it. Then you go through the door with a large red M on it, then whoever you are playing as exits the room as Mario!
Start out in the main room on the ground level. Go up the stairs, through the keyhole door, and up the winding stairs. Go through the door at the top of the stairs, take a right, and enter the the door with the star on it.
You have to get enough stars to unlock the star door(the one where peach is crying out for Mario) and when you beat Bowser you'll get a key for the basement type area. To get there you go through one of the doors underneath the stairs and go down the stairs there and unlock it.Then you get enough stars to unlock the next star door and then you beat Bowser again and then you will get a key for the door leading to the third floor,or second floor in your case.
you need a certain amount of stars
Go in the door beside the door with the 3 stars on it. DON'T go down the stairs, just keep going forward and enter the door.
He is up the stairs you see when you first enter the castle. Then up the stairs you see when you enter that door. Then run around this next room until you see more stairs. Then, when you enter the clock room, run to the left until you hit the wall, then turn around and hop up the giants steps. Then enter the door at the top. Bowser is up the stairs you see at the when you enter. But this requires 70 stars.
well before you unlock Mario you have to earn 8 stars. After you earn the 8 stars go to princess peach's rec room. inside the room you will see a door with a 8 on it. when you go inside there will be a picture of Mario and then you will jump in the picture.
If you mean that door in the rec room in Super Mario 64 DS with the number 8 on it, you just need to get 8 stars and then it will open. The course with Goomboss, who holds the key to the room where Mario is locked, is behind this door.
Enter the castle through the front door, and continue straight forward up the stairs until you reach a locked door. To the right there is another door (opposite the door with the big Star), that requires one Star to unlock. Through this door is the character selection room. Doors in this room lead to rooms where the three human heroes are initially locked up.
Walk into the mario door.