Theory: Paper Mario is Canon to Mainline

Paper Mario games are canon and also happen in the world of mainline Mario games but we see them from the perspective of the Paper World.

Abstract
All Paper Mario games depict events, locations and characters that exist in both a “Real World” and a “Paper World”. The stories are depicted through the “Paper World” and everything still happens in the “Real World” without the “paper aesthetics”.

Chapter 1: Same Universe
All Paper Mario Games happen in the same universe
 * In Paper Mario: The Origami King, Princess Peach’s portrait from all previous Paper Mario games can be seen.
 * Notes belonging to Goombella from Paper Mario: The Thousand-Year Door and Parakarry from Paper Mario 64 can be found in Shy Guy Jungle in Paper Mario: Sticker Star.
 * Paper Mario: The Thousand-Year Door references the events of Paper Mario 64 multiple times and is a pretty direct sequel to it.
 * Super Paper Mario features portraits of Mario’s previous partners in Mario’s House, as well as many Catch Cards featuring characters from previous games.

Regarding the “arts & crafts” focus of Paper Mario: Sticker Star and beyond, the first 3 games also feature plenty of “paper mechanics”. Although not the main focus, they are still present in the story and the world.


 * Paper Mario has:


 * The fact that characters are flat and the way characters turn around.
 * Kammy Koopa being taped into the story.
 * The Star Spirits getting turned into cards.
 * Mario floating down after the veranda falls.
 * Mario floating into bed.
 * A Goomba masquerading as a picture on a signpost.
 * Clouds in the background of Goomba Road battles held up with sticks.
 * The way Mario enters and exits a pipe.
 * Goombas lying flat on top of blocks to hide.
 * Merlee folding Mario into cards when she casts her spell.
 * Stilt Guys falling down as pieces of paper in General Guy’s Battle.
 * Star Kid turning “invisible” by turning sideways.
 * Stairs in the Crystal Palace unfolding from the wall.


 * Paper Mario: The Thousand-Year Door has:


 * The fact that characters are flat and the way characters turn around.
 * Paper Curses
 * Boats turn by flipping around like a piece of paper.
 * The way Mario enters and exits a pipe.
 * The Pipe transition screen.
 * People falling flat when they’re knocked down.
 * The transition from outside to inside buildings.


 * Super Paper Mario has:


 * The fact that characters are flat and the way characters turn around.
 * Flipping between 2D and 3D.
 * Slim’s ability to turn characters “invisible” by turning them sideways. (similar to Star Kid in PM64)
 * Spiny Tromps look like they’re made out of either Wood or cardboard.
 * Sometimes a piece of paper is peeled away to reveal a secret (like a hidden chest, for example).
 * Mimi’s head unfolds like a piece of paper.
 * Mimi says she’ll tear the heroes into little bits, like confetti.
 * The way Mario enters and exits a pipe.
 * The Pipe transition screen.
 * The Brobot’s entrance and battle transition.
 * Rolling Thwomp saying: "I ROLL OVER YOU AND MAKE YOU FLAT LIKE SHEET OF PAPER!"
 * Luigi’s Super Jump.
 * The audience members.

Chapter 2: Paper Stuff in Real Life
As chapter 1 shows, all games are part of the same canon, and all games involve some form of “arts & crafts” mechanic, such as paper folding, stickers, paint, etc. This chapter shows how these mechanics can still exist in the real world.
 * 1. Real World characters can be turned into paper, cut, folded or molded without major consequences

As seen in Mario & Luigi: Paper Jam, the Trio Attacks have the ability to turn real world enemies into paper, then cutting or folding them without any “real world” consequences outside of dealing normal damage.

In Mario & Luigi: Superstar Saga, Luigi is able to be squashed into the shape of a surfboard.

Additionally, in Mario & Luigi: Superstar Saga, Mario & Luigi: Bowser Inside Story and Mario & Luigi: Dream Team, Mario is able to be smashed by a hammer and become smaller, blown up like a balloon or filled to the brim with water.

In Paper Mario: Sticker Star and Paper Mario: Color Splash, it is shown that real life objects can be turned into stickers/cards, and still return to their normal form without consequences.

In the Mario Kart series, characters can be flattened by being crushed by a player with a Mega Mushroom or by obstacles in the track


 * 2. Stickers

Stickers are not natural to the Mushroom Kingdom. Stickers come from the Sticker Star, and rain down over the Decalburg region once a year when the Sticker Comet arrives.


 * 3. Paint

The Paint found in Paper Mario: Color Splash is not your everyday Paint. Paint is consistently described as a life force throughout Paper Mario: Color Splash:
 * “You know... paint! That colourful stuff coursing through our bodies?”
 * “The paint you just absorbed is basically my blood, sweat and tears.”
 * “Paint adds beauty and life to the world.”
 * “Where exactly are we supposed to find this magical, life-giving paint you speak of?”
 * “I did basically sacrifice my lifeblood to get you out of that pickle back there...”
 * “They’re sucking the very life out of this beautiful island!”

It is also not something that’s exclusive to the Paper Mario World. As theorised in Seán D. Walsh’s High Consensus Theory on Goo, Paint appears as a sort of “life force” in various games that take place in the real world, such as Super Mario Sunshine & Luigi’s Mansion. When real objects (things) are wrung out in Paper Mario: Color Splash, they too produce paint, proving that paint is not a substance exclusive to the Paper World.


 * 4. Battle Cards

Battle Cards are the main battle mechanic that’s used throughout Paper Mario: Color Splash. While the cards may seem like a somewhat papery inclusion, Battle Cards also appeared in the real world in Mario & Luigi: Paper Jam.

Chapter 3: Continuity
Chapter 1 proves that all Paper Mario games share the same canon. Chapter 2 proves that no major paper mechanics would “break” real world canon. All that is left is to prove that both canons share the same world/stories: *Mario & Luigi: Paper Jam shows that both Paper characters and real characters have lived almost identical lives, with shared experiences.
 * Goomboss, who was created by Bowser using the Star Rod in Paper Mario 64, also exists in Super Mario 64 DS and Mario Kart DS, both events that happened in the real world.
 * Dry Dry Desert exists in both the Paper world and the real world, as well as the Dry Dry Ruins, which were discovered during Paper Mario 64.
 * Peach’s/Bowser’s flying castle from Paper Mario was created by Bowser using the Star Rod. It reappears in ''Mario Kart: Super Circuit’s Rainbow Road.
 * Goombette from Super Mario Odyssey is pink, just like the other female goombas only previously seen in the Paper Mario Series, such as Goombella or Goombaria.
 * Snowmen from Paper Mario reappear in the Mario Kart series with the very same design.
 * A Red Chain Chomp - originating from Paper Mario: The Thousand-Year Door - appears in a movie projected by the WarioWare: Touched! souvenir “Reel-to-Reel”.
 * Koopatrol Armor from Paper Mario appears in Bowser’s Villa in Super Princess Peach.
 * Koopatrols themselves appear with their designs from Paper Mario: the Thousand Year Door in Mario Pinball Land.
 * Hammer Bros. appear with their design from Paper Mario in Mario Kart: Super Circuit's award ceremony.
 * The “Headbonk” move that Goombas perform in the Paper Mario series returns as an attack in Minion Quest: The Search for Bowser and Bowser Jr.’s Journey.
 * Star Hill appears in Mario & Luigi: Partners in Time, referencing Paper Mario.
 * The 7 Star Spirits from Paper Mario reappear in Mario Party 5.
 * The “Snow Bunny” item from Paper Mario: The Thousand-Year Door & Whackas from Paper Mario appear in Mario Party 6 on the Board “Snowflake Lake”.
 * On the Pyramid Park board of Mario Party 7, a Bowser Sphinx appears with Tutankoopa’s Headdress from Paper Mario.
 * The scoreboards of Mario Golf: Advance Tour and Mario Golf: Toadstool Tour feature many characters that Mario wouldn’t have met without the events of Paper Mario taking place:
 * Goombario, who Mario met when he ended up in Goomba Village after he fell out of Peach’s Castle in the intro of the game.
 * Kooper, who Mario met when he took a trip to Koopa Village on his way to free Eldstar from the Koopa Bros. Fortress.
 * Bombette, who Mario met when they were both locked in the dungeon of Koopa Bros. Fortress.
 * Moustafa, who Mario met for the first time in Dry Dry Outpost when he was trying to unearth the Dry Dry Ruins and free Mamar. Moustafa was also hiding his identity as “Sheek” before he met Mario in Paper Mario.
 * Tubba Blubba, who Mario had to fight in Gusty Gulch to free the Boos and get Skolar back from Lady Bow. After he’s defeated by Mario, Tubba Blubba vows to be good from then on.