Dreamy Neo Bowser Castle is a dark level where images of Bowser appear in the background. There are also areas with lava located in certain areas.
The Pi'illo that must be rescued takes Mario to an outside area that resembles Mushrise Park and has the Dreamy Mushrise Winds theme.
Mario and Prince Dreambert head into Dreamy Neo Bowser Castle to 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 an 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 plenty 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. This area is not accessible in the overworld, since Antasma specifically created it for his battle.