I can’t think of any truly rare skill, but my semi-rare skills are:

• I can identify many species of wild animals and plants (reading lots of field guides and taxonomy books)
• I have research skills related to optics, chemistry, biochemistry, etc. (from academic studies up to PhD)
• I can play my hands like a flute (lots of practice, to the detriment of those around me)
• Clone and grow mushrooms (YouTube videos and online forums)
• Put my legs behind my head (No idea. I am not very flexible but this specific thing I can just do)
• I am currently working to develop my electronics skills by reading, watching videos, and building projects at home.