they can become a 2D shadow at-will and stick to a flat surface, In this form they don’t occupy space, they can slip through any small crack and can walk on walls and ceilings. they still get damaged by 3D stuff though, and anyone can grab them and rip they back into 3-d space. Think of it like turning into a super flat slug, or just like that zelda game 'link between worlds' where link can turn into a picture.
shadow people are poor immigrants. There’s big discrimination against them cuz theyre not seen as being “real” like other people are, so they can’t get married or inherit property. they can only legally work as entertainers and artists. (both of these are vague terms though, a bartender is technically an entertainer, any kind of craftsman is an “artist”) People only want to hire them as assassins and spies.
They live in paper lanterns, their ghettos strung together and hung above the neighborhoods of 3D people. Rarely a shadow person will come into some money, build a house with paper walls and sliding doors, and let dozens of their poor relatives live with them in crowded conditions. Visitors to these shadow homes are weirded out by how there’s no furniture; and how they eat dust and cobwebs and drink light
if you wanna play one do race as class, your just like a rogue or a halfling but you get the 2D form ability at will.