Selkie Sealskin

A selkie's sealskin contains some of the selkie's magic, although only the selkie is able to use that magic (which allows them to change into a seal when they put on the skin). 
For anyone other than the selkie, if they hide the skin, they are able to keep the selkie from changing into a human form, thereby trapping them on land.
While it may be possible for the selkie's descendants to use their skin (if these descendants are part human and have none of their own), the opportunity for this happens so rarely that it has not been positively confirmed.

Item type

Magical