Bowser's Sky Castle

Bowser's Sky Castle is World 6-3 and the final level of Paper Mario: Sticker Star.

Mario first discovers the castle at the Gate Cliff after finding the other five Royal Stickers. By using them to flip a portion of the wall, the castle is unveiled. However, immediately after the castle flies up into the sky. After defeating Bowser Jr. on his airship, Mario reaches the castle.

Layout
Mario starts at the castle's front entrance, right outside. Entering the castle, the first room is a lengthy hallway. At the end is a door; opening the door reveals Kamek, who battles Mario. Defeating him allows access to the second room.

The next room contains a conveyer belt-like carpet that activates when Mario steps on it; as soon as he does, it begins to roll up behind him. Additionally, the carpet is full of holes, and on the underside is a pit of spikes. Touching the spikes sends Mario back to the beginning of the room, and the carpet resets. The carpet also has several bars along it that serve as obstructions, with one that is higher up but briefly moves down. At one point, the carpet stops, and the platform takes Mario to another platform. As soon as he steps off, the carpet falls into the pit below.

In the next area, Mario and Kersti find Princess Peach, taped to a chain. Before Mario can peel the tape off, Bowser appears, who unveils a long hallway and challenges Mario to a battle. After defeating him, however, he falls off the tower at the end of the area, with the Royal Sticker. Seconds later, though, he returns as a giant made of cardboard. As soon as he is defeated like this, he returns to his normal state, allowing Mario to save Peach.

By the time Mario defeats the Giant Bowser, the castle has mostly been destroyed. As the game then cuts to the Sticker Fest, the castle's outcome is unknown.

Bosses

 * Kamek
 * Bowser

Enemies assisting Bowser

 * Koopa Paratroopa
 * Bony Beetle
 * Spike Top
 * Hammer Bro
 * Fire Bro
 * Boomerang Bro
 * Piranha Plant
 * Fire Piranha
 * Swoop
 * Whomp
 * Lava Bubble
 * Chain Chomp

Area Tattles

 * Entrance: "An entrance made of your own face... Boy, this guy's got some bad taste."
 * First room: "It feels like... the finale, doesn't it? To be honest, I'm a little nervous."
 * Second room: "One taste of those spikes below, and you're done for! Talk about a poor interior-design choice!"
 * Third section: "Bowser's face is on the floor too? This guy's got zero design sense."

Super Smash Bros. series
In Super Smash Bros. for Nintendo 3DS and Super Smash Bros. Ultimate, there is a stage based on the Paper Mario series called Paper Mario which combines elements from the series. Bowser's Sky Castle is used as the third stage tier. The giant Bowser head doorway acts as a platform, where players can stand on top of the head and in the mouth. Two hovering platforms that move up and down are placed at both ends of the stage. There is no solid ground below this section of the stage. The Bowser head platform acts as a main hazard, where it is able to rotate and occasionally unable to be used as solid ground. The mouth is also capable of closing, damaging and launching any fighter trapped inside.

Trivia

 * It is the only time in the Paper Mario series where the castle contains no regular enemies and instead only bosses, save for those assisting Bowser.
 * The castle's level marker stays red even if the player completes the game. It is, however, shown as blue in the Prima guide.
 * The castle was planned to have mini-games to lengthen the level, but the idea was scrapped due to time constraints.
 * Kersti says that when falling into the spikes below in the second room, Mario is done for, but touching the spikes results in losing 1 HP, and the player must start the second room all over again.