Ztar

Ztars are items that appear in the Mario Party series. They are the opposite of Stars, as they will subtract Stars from a character's Star amount when obtained. Ztars are earned by landing on a Ztar Space and once a character does so, Bowser will appear and will give the captain a Ztar in exchange for coins. This happens in Mario Party 10 and Mario Party 11. In those two games, Ztars are worth 30 coins each.

Ztars are actually Stars that became corrupted by Bowser and Bowser Jr. using the particles from the black vortex they used to steal the Stars. They did this as a way to hinder Mario and his group from retrieving the stars. It is unknown why they would do this, as Bowser said that he wanted Stars to decorate his castle.