Dream's Deep
Dream's Deep (known as ???? on the save screen) is an area in Mario & Luigi: Dream Team that's the core of the Dream World. It's a very short area where the bros. find Antasma and Princess Peach, and it's also where the Bros. fight Bowser and Antasma in his bat form.
They learn about the Ultibed and how to use the Luiginary Ball in the overworld, as well as the Ball Hammer and Hookshot, later in the game.
In Dream's Deep, various messages from Luigi are shown, which consists of Luigi's thoughts toward his brother, his feelings, and his wills. Along with the messages are various images of Luigi.
This is the only area where Dreamy Luigi can activate his alternate mode - his thread form. It is also the only place you can battle Dark Blocks - monsters that takes the shape of a dark ? Block..