This is a set of clothes or accessories for figures.
From the Good Smile Company website:
The Nendoroid More series is a selection of items created to make Nendoroids even more enjoyable, and the latest addition to the series is a new face parts case with a Halloween theme!
The case allows you to store up to two spare expression parts inside while also having a cute black cat appearance with a Halloween theme to put on display - which means that even your spare parts will have a place in your collection!
Note: Images shown here are for illustrative purposes only. No Nendoroid expression parts are included with this product. Certain face plates may not fit into the parts case depending on the character design.