World 6 (Paper Mario: Sticker Star)
From the Super Mario Wiki
World 6 is the sixth and final world found in Paper Mario: Sticker Star, located north of the Decal Channel. It takes place in the sky, and has the three levels (making it the shortest world in the game) that take place at a rock formation out at sea, an airship, and Bowser's Castle. Additionally, only the Gate Cliff may be accessed with the boat; to reach the other two levels of the world requires the assistance of Flutter. Rocky Wrenches make their debut in 6-2, and Hammer Bros. and their sub-species are common enemies. Bowser Jr. and Kamek are also fought for the final time. The world's boss is Bowser, making him the final boss in the game.