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Nightmare Fuel: Shantae
Just to the east of Oasis Town is... well, in-game it's described as a "swamp", but the area looks more like something inspired by some nightmare one of the developers had as a kid. It's practically a small-scale Eldritch Location, with its amorphous black-purple blob creatures and pod-covered trees/columns/somethings topped off with what appear to be giant (five times Shantae's size giant) bugs of some sort. Considering the entire rest of the game up to that point had been fairly standard field/forest/desert environments, this one especially sticks out. The same lighthearted background music continues to play throughout the area, but that arguably just makes things worse.