When the sparkles appear in a loading screen, press the Cursor Keys to move them around.
The Dressing Room is available after you have 3,000 points.
While in a lobby, press [Down] + [Left] + [Right] to create a Photon Chair. Press A or D to turn the chair, [Down] to move it forward, or [Right] to get out of it.
The Ranger Wall is available in Galleon's shop after you have 300 points if you are playing with a Ranger class character.