Blind Box Toys
This comes from the Pop Mart website:
“BLIND BOX” is a type of sealed packaging that keeps what’s inside a mystery until you open it.
Every design of the figures in the series will be displayed on the side of the box, and you will be getting one of them once you open the box.
Some are rarer to find, which we call the “SECRET” figures.
Take The Monsters “TOYS” series, as an example:
This is an interesting article on the phsychology of surprise: Why Do Kids Love Blind Bag Toys? The Psychology of Surprise