Neo Bowser Castle is mainly a large, dark castle that has many of Bowser's features including statues with his face on them, fire, and lava. It also shares Antasma's features including many dark-vain like objects that is later revealed to help power the castle. Also, enemies including Flaming Antasmatons, Fire Bros., and Walker Guys with Chain Chomps are the main enemies encountered in the castle.
In Mario & Luigi: Paper Jam, Neo Bowser Castle now has giant rockets at the bottom that allows it to maintain flight thanks to the ore harvested from Twinsy Tropics. The interior is also very similar to the one from Mario & Luigi: Dream Team.
Neo Bowser Castle is first created after Antasma used the Dream Stone to create it for Bowser as part of their agreement. The castle is then lifted into the sky where it is surrounded by a barrier forcing Mario, Luigi, Prince Dreambert, and the others to find a way to shatter the barrier. They eventually enlist the help of The Zeekeeper where he uses his Wake Beam to destroy the barrier. Mario, Luigi, and the rest all enter in but Kamek halts their process by mixing up the paths. Antasma then shows up and opens a portal to the dream world where Kamek makes his escape into. Prince Dreambert suggests heading into there after him in order to fix the paths. Mario has to enter Dreamy Neo Bowser Castle two more times in order to finally get somewhere. After passing more puzzles, they eventually reach a room where Bowser is sleeping on a pillow of Antasma. However, there is another barrier that prevents Mario and Luigi from interfering but Prince Dreambert remembers the idea of entering another one's dreams since Big Massif at Wakeport. Luigi then falls asleep where Mario enters back into the dream world to confront Bowser.
Neo Bowser Castle was first made after the Bowsers (Bowser and Paper Bowser) harvested enough ore to power it up. They decided to take flight after Mario, Luigi, and Paper Mario rescued Princess Peach and Paper Princess Peach and defeated their respective sons (Bowser Jr. and Paper Bowser Jr.). The Bowsers then assaulted the Mushroom Kingdom wrecking Princess Peach's Castle in the progress. The Bowsers then decide to station over Mt. Brrr planning their next form of attack. Eventually, the Marios, Luigi, and Starlow managed to make it onto Neo Bowser Castle a second and final time to confront the Koopa Kings in a showdown. However, their process was hindered by the Kameks and the Koopalings whom the heroes all defeat. The Bowsers finally engage the heroes in a final battle where, even after transforming, the Bowsers were defeated.