This product is a kitchen goods for making "skull" type boiled eggs. Peel the boiled egg, fit it in a mold, and soak it in cold water for 2 to 3 minutes to instantly make a skull-shaped boiled egg.
It's priced at $ 11.99 and is available from the official BFF Toys shop on Amazon.com. However, unfortunately, it is not delivered to Japan.
By the way, from the shop, it is recommended to purchase a set with "Funny Side Up", which is a type that makes a "skull" type fried egg by placing it on a frying pan and dropping the egg. It wouldn't be a bad day to start with such a funny breakfast.
* All images are from BFF Toys