Black Bowser's Castle

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 accidentally opens leading to a cell instead. Huey admits that Bowser caught them, but he also states how they're 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. After Roy is defeated, he returns all of the stolen paint and the 1-Up Mushroom cards back to Mario and the door in the pit leads him and Huey to a factory, where all 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 Bowser's throne room, with Peach now hanging above the throne. Black Bowser taunts them, telling him that he wasn't 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. After Mario uses him, he can now absorb Bowser's black paint, so he can't heal himself. After Black Bowser is defeated and Peach is repainted, the castle begins to collapse, due to the 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 castle, removing the black paint, and transforming it into a card.

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

Enemies

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

Trivia

 * This is Bowser's third floating castle in the Paper Mario series, the first two being his castle from the original Paper Mario and Bowser's Sky Castle from Paper Mario: Sticker Star.
 * 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.