Super Mario Maker's Mystery Mushroom costumes all have a debut source material listed for each character, but this was handled in a strange and arbitrary manner. On average, most characters are listed with their first localized source material, but many outliers and oddities exist:

• Luigi and Trampoline are both listed as debuting in Super Mario Bros. instead of Mario Bros. and Donkey Kong Jr. respectively.
• Toon Link is listed as originating from The Legend of Zelda: The Wind Waker instead of The Legend of Zelda: Four Swords.
• Undodog is listed as debuting in Super Mario Maker instead of Mario Paint.
• Toadette (in the Captain Toad: Treasure Tracker outfit known in later games as "Archivist Toadette", and despite not being distinguished as a separate character like Captain Toad is from other Toads) is listed as having originated in Captain Toad: Treasure Tracker instead of Mario Kart: Double Dash!!
• The Generation I Pokémon included in the base game are listed as only originating from Pokémon Red Version and Pokémon Blue Version, whereas Pokémon Yellow Version is listed as the debuts for Charmander, Squirtle, and Bulbasaur alongside the other two games.
• Wario, Yoshi, Captain Toad, and Shaun the Sheep are listed as debuting in their first spin-off series roles (Wario Land: Super Mario Land 3, Super Mario World 2: Yoshi's Island, Captain Toad: Treasure Tracker, and the TV series Shaun the Sheep respectively) instead of their debuts (Super Mario Land 2: 6 Golden Coins, Super Mario World, Super Mario Galaxy, and the Wallace & Gromit short film A Close Shave respectively).
• Mr. Game & Watch, Babymetal, Hello Kitty, and My Melody are listed under their respective brand names, which contrasted against other characters has them listed as originating from works that do not exist. To an extent, this also applies to R.O.B., the Mercedes-Benz GLA, and Diskun.