You can trade off your mysterious shells for figurines

Someone in Hyrule Town has a slot machine and the machine uses mysterious shells, found throughout Hyrule, you can bet up to 3 and try your luck at finding a figurine, with 130 to be found, 6 at the end

Treasures in The Minish Cap take the form of rupees, kinstones and mysterious shells

Mysterious shells

Visiting the sculptor's shop, Link could get chances to earn these figures by exchanging mysterious shells with him