Just before entering Peach's Castle towards the end of the game, there's a brief moment where the L on Luigi's cap is mirrored.
After defeating the Water Vellumental, Olivia says, "Look, Mario! it turned into a Bibliofold!" The miscapitalized "it" is part of the English script.
In the English version, Olivia refers to the Sea Chart as a See Chart at a certain point in Scorching Sandpaper Desert. This is not set up as a joke nor commented on, so it seems to be just a mistake.
Content Leak: The game was hinted at by Sabi, who was infamous for leaking numerous E3 2019 plans and almost leaked Nintendo’s own plans before being stopped by lawyers, all the way back in January 2020. The game itself was then leaked a week before release, with dedicated discussion platforms being forced to combat them.
Executive Meddling: An interview released the day before the game came out talked about how, from Sticker Star on, they were no longer able to create original characters like the Goombas or modified Toads seen in past games or reuse such characters from past gamesnote It is unclear if the creative team meant just classic Paper Mario characters of mainline species are banned and other classic characters with fully unique designs like Vivian or the Pixls can return, or if all of them are banned even if they meet the rules or are altered to do such, though Woody’s return in Mario Party Superstars as well as Vivian having a spirit in Super Smash Bros. Ultimate suggests the former. Instead, they must either use pre-existing designs for characters and slightly modify them, such as Toads with various outfits, or create completely unique characters divorced from the franchise's usuals, such as Olly and Olivia.
God Never Said That: After the pre-release interview revealing the restrictions, fans mistook one of them to mean specific original characters couldn’t be reused across games even if they met the rules. What producer Kensuke Tanabe actually said was even if Olly and Olivia weren’t seen after Origami King, he hoped they would stay in the hearts of the fans. The game itself features the returning Sombrero Guy in a bigger role and a namedrop for Kersti, while the previous game featured the explicit return of the Snifit or Whifit host for a stage, further demonstrating the misunderstanding and some wiggle room. Said statement and example was likely only worded that way to avoid spoiling Olly & Olivia permanently dying at the end of the game.
Orphaned Reference: One room in Bowser's Castle contains weapons used by Spikes: their spike balls, and their spiked rollers from Super Mario 3D World. While origami Spikes in this game can spit up and throw spike balls, the rollers are never seen. Despite this, there's a Dummied Out model associated with them that depicts this same roller.
This game is notable for being the only Mario RPG where Bowser is never directly fought in the entire game. Even in previous RPG games where Bowser did an Enemy Mine with Mario, he was still fought at least once before then.
by Sabi, who was infamous for leaking numerous E3 2019 plans and almost leaked Nintendo’s own plans before being stopped by lawyers, all the way back in January 2020. The game itself was then leaked