Dreamy Neo Bowser Castle is a dark level where images of Bowser appear in the background. There is also areas with lava located in certain areas.
Mario and Prince Dreambert head into Dreamy Neo Bowser Castle to first chase after Kamek. Joined by Dreamy Luigi, Mario and the rest go through different trails and reach Kamek. However, Kamek escapes twice but is eventually defeated a third time. Mario and the rest head into Dreamy Neo Bowser Castle in attempt to wake up Bowser who is napping on Antasma. Mario, Dreamy Luigi, and Prince Dreambert all confront Bowser (well, actually Dreamy Bowser) and the chase begins. Dreamy Bowser eventually finds himself cornered and eats plently of meat and turns giant. Confident, Dreamy Luigi turns giant himself and defeats Dreamy Bowser in a long and difficult battle. Mario and Prince Dreambert then leave Dreamy Neo Bowser Castle.
Mario eventually has to enter Dreamy Neo Bowser Castle again to fight Antasma and defeats him once and for all.