Black Bowser's Castle

"We've got to stop them from making more black paint. Let's get back to that factory and destroy it!"

- Huey

Black Bowser's Castle is the final area in Paper Mario: Color Splash. It is on a floating island with an appearance similar to that of Bowser's Sky Castle, but with pipes leading into the rock. A rainbow road, leading up from the Prisma Fountain in Port Prisma all the way to here, is unlocked once Mario has retrieved all six Big Paint Stars.

Layout
The castle's entry hall consists of a hallway, where a portrait of a color-drained Princess Peach is initially seen, just out of reach. When Mario attempts to lower it, however, a trapdoor opens leading to a cell instead. Huey admits that Bowser caught him and Mario, but he also states how they are not surrounded by "bad guys". Six Slurp Guys appear, followed by Roy Koopa, leading to a battle between them, but not before they steal all of Mario's paint and his 1-Up Mushroom cards from him. After successfully defeating Roy, Mario recovers all of the stolen paint and the 1-Up Mushroom cards and the door in the pit leads him and Huey to a factory, where all of the paint stolen from Prism Island is brought to mix into black paint. The black paint is later used to color dangerous weapons, such as Banzai Bills and Bob-ombs, which Black Bowser intends to use to paint the world black. Mario manages to destroy the tank holding the black paint by blowing up Giant Bob-ombs, which floods the entire factory. The factory also has a warp pipe leading Mario and Huey back to the entry hall.

Behind the wall where Peach's portrait was is a hallway leading to Black Bowser's throne room, with Peach now hanging above the throne. Black Bowser taunts Mario and Huey, telling him that he was not expecting him to make it this far and battles them. After the black paint is finally removed from his head, the real Bowser is briefly freed from the black paint. However, it takes control of him once again, leading to the true final battle. Bowser will now have the black paint return back to him after all of his attacks, rendering the fight nearly impossible to win. Huey decides to change back to his original form by transforming into a card. When Mario uses him, Huey can absorb all of Bowser's black paint, so he cannot heal himself. After Mario successfully defeats Black Bowser and repaints Peach, the castle begins to collapse, due to the incoming black paint. Mario, Luigi, and Peach escape back to Port Prisma, while Huey stays behind and to ensure that all the black paint does not fall onto Prism Island, squeezes the remains of the castle, removing all of the black paint, and transforming it into a card.

In later battles, the Black Bowser's Castle card summons the castle and crashes it into the opponents. It is also powerful enough to severely damage Black Bowser in battle and instantly defeat common enemies.

Enemies

 * Bob-omb
 * Hammer Bro
 * Ice Bro
 * Boomerang Bro
 * Fire Bro
 * Sledge Bro
 * Slurp Guy
 * Slurp Snifit
 * Paint Guy
 * Roy Koopa (boss)
 * Black Bowser (final boss)
 * Black Lava Bubble

Required Thing(s)

 * Washing Machine (to clean up all the black paint during Roy's boss battle)
 * Huey (used to absorb black paint during Bowser's boss battle)

Trivia

 * Black Bowser's Castle is tied with the Green Energy Plant for the least amount of colorless spots in the game, with only one, and that colorless spot is Peach herself.
 * In Rescue V: Fearless Color Defenders, the Rescue Squad Chief shows scenes of Black Bowser's Castle, but is instantly scolded by Rescue Red for showing spoilers.