The Bitlands

The Bitlands is an extremely pixelated (to the point of it being named after such) dimension located beyond the yellow door in Super Paper Mario. According to The InterNed, the overworld music of The Bitlands is titled "The Open Plane", and the music in the underground area beneath the two red pipes is titled "Nostalgic Underground", due to it being an altered version of the classic underground theme from Super Mario Bros.

The Bitlands
When Mario and co. reach the Bitlands, Tippi is kidnapped by Francis who then takes her to his fort. In the search for Tippi, the group finds its way through many obstacles, including an encounter with a gigantic Koopa Troopa. Soon after, Mario discovers a makeshift fort populated by the remnants of the Koopa Troop. It is discovered that their leader is Bowser, who decides to fight Mario. The Koopa King loses and joins Mario's party after a humorous conversation. The heroes then continue on to the Tile Pool.

Stages in The Bitlands

 * Chapter 3-1: When Geeks Attack (The Bitlands)
 * Chapter 3-2: Bloops Ahoy (The Tile Pool)
 * Chapter 3-3: Up, Up, and a Tree (The Dotwood Tree)
 * Chapter 3-4: The Battle of Fort Francis (Fort Francis)

References to Other Mario Games
The Bitlands (especially Chapter 3-4) holds many references and similarities to older Mario games or other Nintendo-related things. These include:
 * Francis has a Famicom (a Japanese NES), an SNES, a Virtual Boy, an N64, a GameCube, a Game Boy, and (if the player switches to 3-D) a Wii.
 * Francis has a huge amount of posters showing Lady Bow and Bootler (this marks Lady Bow's second cameo appearance in Super Paper Mario), Petuni, Princess Peach, and other, less identifiable characters.
 * Mega Koopa is identical to a Koopa Troopa from Super Mario Bros. on the NES. They are also huge, a possible reference to the Gargantua Koopa Troopa from Super Mario Bros. 3, and it is also a reference to the Mega Goomba from New Super Mario Bros.; a regular Goomba enemy that grabs a Mega Mushroom and gets big.
 * A Blooper is a mini-boss in the Tile Pool; Bloopers have had at least a mini-boss role in every Paper Mario game to date
 * Bowser declares that there will be no more sequels; many Mario games have at least one sequel, and Bowser gets defeated in both Paper Mario sequels.
 * Francis is a big fan of Mario reference-filled TV shows, one of which involves Tubba Blubba (making every Paper Mario game to date have a giant Clubba at least mentioned in their corresponding Chapter 3s); another involves X-Nauts, and yet another involves Sir Grodus.
 * The underground cavern in 3-1 is an almost exact replica of World 1-2 in the original Super Mario Bros. The only differences are some of the power-ups have been changed, and a small area has been removed.
 * The overworld music has several interludes in which segments of the Super Mario Bros. theme may be heard clearly.
 * The player must take the second pipe in the Warp Zone look-alike area to continue the sub-chapter, which may be a reference to Super Mario Bros. when Mario or Luigi must take the second pipe in the Warp Zone to go to World 3, which is the world the Bitlands is.

Trivia

 * When Mario comes to a part of Chapter 3-1 with all the colorful blocks, if he flips, he can see they are really simple poses of block statues.
 * The Bitlands is also one of only two worlds where there is at least one boss in each section, (Bowser in 3-1, who joins Mario's party after being defeated, Big Blooper in 3-2, Dimentio in 3-3, and Francis in 3-4), with Castle Bleck being the other world.
 * Furthermore, including the optional Pixl's Barry and Tiptron, the player gets four Pixls in the Bitlands, which is more than in any other world in Super Paper Mario.

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