The area around it’s face, resembles a helmet with horns. Much like Nightmarchers who wear armour as they marched through the night to ancient battle sites. Lastly Marshadow is a fighting/ghost Pokémon, likely a direct nod to these mythical warriors -S

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Marshadow always hides in the shadows, and is scarcely seen by humans. Menehune would only ever come out at night and is also rarely seen by people. Menehune were known to be superb craftsmen, building their masterpieces at night.

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