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
Black Bowser's 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 and Mario are ambushed by six Slurp Guys, and Roy Koopa. At the start of the battle, Mario's paint is drained by the Slurp Guys, and Roy uses a cannon to fire it back at him. After taking enough damage, Roy orders Paint Guys to put all their paint in his cannon, then mixes it up to create black paint. Mario must remove the paint with the Washing Machine Thing, and then defeat Roy by dealing enough damage.

A door leads Mario 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 must go on the conveyor belt, defeat a Paint Guy, and then stand in its place. Summoning Huey, Mario asks him to act as a bucket so they can progress.

Continuing on the conveyor, Huey sees that Bowser is producing black paint bombs. Mario can escape the conveyor belt by sliding down a Goal Pole. Huey observes Giant Bob-ombs and suggests that they blow them up to stop the black paint. To destroy the crates in his way, Mario must knock Bob-ombs down and get them to blow up. Soon, he is ambushed by a Hammer Bro, a Boomerang Bro, Fire Bros., and Ice Bros. Once they are defeated, Mario can guide some Bob-ombs to the giant ones, causing a chain reaction that explodes the factory. The black paint slowly begins rising, and Mario must escape before it touches him.

In the next room, Mario must run from a flood of black paint to escape into a Warp Pipe leading back to the entry hall. Peach's portrait is gone, and a purple rope appears instead. Pulling it opens a door into another hallway, where Huey tells Mario that he will always be grateful for their friendship. In Black Bowser's arena, Peach's portrait is hanging over his throne, and he challenges Mario.

As Black Bowser takes damage, the black paint layer slowly disappears. Eventually, he looks around in surprise and asks Mario if Peach is with him. The black paint then overtakes Bowser and he enlarges in size. Any damage Mario does during the next turn is restored through Black Bowser re-absorbs black paint. To combat the black paint, Huey transforms himself into a Battle Card, turning him 3D again. Mario must use Huey to block Black Bowser's attacks and absorb the black paint.

After taking enough damage, Bowser spits out all his paint for one final attack. If Mario blocks this, Bowser is severely weakened and will be defeated by the next attack. The castle starts crumbling as black paint rises. First, Mario must repaint Peach, and then run out to the castle's entrance. Luigi gets Peach and Mario safely on his cart, but Huey refuses, saying that he has to prevent the black paint from spilling again.

Huey squeeze Black Bowser's Castle into a card, which drops down from above. Back in Port Prisma, Luigi, Mario, and Peach have safely returned and Toad notices the card. Huey comments that he has to take the black paint far away, flying into the sky and disappearing. Everyone celebrates the return of the Big Paint Stars, and Peach reassures Mario that Huey is still out there, watching over them.

Enemies

 * Bob-ombs
 * Hammer Bros.
 * Ice Bros.
 * Boomerang Bros.
 * Fire Bros.
 * Sledge Bros.
 * Slurp Guys
 * Slurp Snifits
 * Paint Guys
 * Roy Koopa (boss)
 * Black Bowser (final boss)
 * Black Lava Bubbles

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. However, in Black Bowser's Castle, this does not count towards colorless spot completion.
 * 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.