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Since the games' code overrides TPC, shouldn't Serebii list Shiinotic as Mythical on his website?
"In Pokémon Scarlet and Violet, Shiinotic is defined internally as a Mythical Pokémon instead of Marshadow. This is likely due to a typo between their internal names, with マシェード MASHEEDO (Shiinotic / Mashēdo) being mistaken for マーシャドー MAASYADOO (Marshadow / Māshadō)."