Tales have been told of an ancient culture in these lands, which would banish their wrongdoers by turning them into vile beasts, cursed to terrorize the wilds for the rest of time. Today, many cursed relics used for such purposes are still said to reside amongst the caves unknown...

...most of these sites have already been identified by local researchers. Notably, while these shrines do have transformative power, those transformed don't actually become "vile beasts". They are simply transformed, memories and personality preserved. (It is generally understood that the "becoming vile" part of the ancient tales are due to these transformation being also accompanied with scorn and exile.) However, further study is difficult, given how quickly these relics' transformative properties affect nearby individuals.

Researchers (and other reckless explorers) who dare to visit often return as relatively sane... by pokemon standards. Research visits generally aren't advised, as it's kinda hard to decipher data from frantic notes scribbled by a writer losing dexterity and brainpower. Former humans do often appear in nearby studies as assistants. Though their experiences make them valuable, them being pokemon both physically and mentally often hinders their ability to make records or do other basic human tasks.

The above doesn't exactly stop people from visiting (and getting transformed) anyways.

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Cursed relics are indeed a trope. Figured I had to make one of these with eelektross eventually.