Dream's Deep
Dream's Deep (known as ???? on the save screen) is an area in Mario & Luigi: Dream Team that is the core of the Dream World. It is where Mario and Luigi find Antasma and Princess Peach, and it is also where the Bros. fight Bowser and Antasma in his bat form. Upon their second visit, they learn how to summon the Zeekeeper through the Ultibed and how to use the Luiginary Ball in the overworld, as well as the Ball Hammer and Hookshot during their second visit. It can be accessed from either Dreamy Pi'illo Castle or Dreamy Mushrise Park via portals.
History
In Dreamy Pi'illo Castle, Antasma breaks open a way to Dream's Deep and takes Peach there shortly after Mario defeats Dreamy Mario, the ground sealing up Antasma's escape route as soon as he departs with her.
Mario, Luigi and Prince Dreambert first make their way to Dream's Deep when Eldream (with the help of Dreambunny) drills a hole in Dreamy Mushrise Park, causing a portal to Dream's Deep appear, which the Bros. then enter.
Inside Dream's Deep, Luigi cannot directly aid Mario this deep, and thus, only 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 that appear throughout. Just before Mario goes through a portal leading to the room Antasma and Peach are located, Dreamy Luigi appears, having been able to reach Mario in his usual form.
Heading through the portal, Mario and Luigi confront Antasma holding Peach captive, but as soon as they do, Bowser appears through a portal behind Antasma and Peach, having entered the Dream World after catching the scent of Peach's perfume from the Real World. After Bowser easily punches Antasma away, he prepares to do battle with Mario. Antasma interrupts this, stating that he'd rather use Bowser's power rather than Peach's, and proposes they work together. Antasma eventually convinces Bowser and powers him up in his subsequent battle against Mario.
After the battle ends, Bowser breathes a very powered up flame at Mario and Luigi, knocking them both unconscious. Antasma and Bowser leave Mario, Luigi and Peach lying there and head to the Real World after Bowser is told they'd come back for Peach later. Eldream finds the group, and knowing it was dangerous to sleep in a dream, warps them all back to the Real World.
Much later in the game, Mario and Luigi return to Dream's Deep through a portal in Dreamy Pi'illo Castle while looking for the Zeekeeper and how to summon him. After re-activating a Zeekeeper statue through turning on three switches, the Bros. learn that they must collect the Ultibed parts and give them to a Bedsmith to build the Ultibed, the only way for them to find the Zeekeeper to help them break Neo Bowser Castle's near-indestructible barrier.
