Ztar

From the Super Mario Wiki

The Ztar in the Mario Party series.

Ztars (also known as Dark Stars, previously also Shadow Stars) are black counterparts to stars found mostly within the Mario Party series. Instead of granting the player a star, it takes away one in the player's possession.

Ztars first appears Super Mario RPG: Legend of the Seven Stars when the special attack Dark Star is used. They later appeared in Mario Party, where a Ztar is the Bowser Bogus item for Mario's Rainbow Castle. In this game, it does not count as a negative star. Mario Party 4 features a Ztar hosting the volleyball game in Thwomp's Backroom Ball.

Ztars were renamed as Shadow Stars during the events of Mario Party 6. In Clockwork Castle, if Bowser encounters a player, he will give the player a Shadow Star if the player has one or more stars. This will cause the player to lose all of his or her stars and if there are no stars present, Bowser will give him or her a Special Shadow Star. Bowser will also give the player a Shadow Star if he or she lands on Bowser's Battle Yacht in Castaway Bay. Shadow Stars also make a minor cameo in the comparison quiz section of Speak Up.

In Mario Party 7, they were again renamed to Dark Stars. In one of the ? Spaces in Grand Canal, the player must choose a chest after the chests are randomized by a Blooper. One of the chests holds a Dark Star. If the player chooses this chest, he/she must take it. In Neon Heights, at Bowser Time, Bowser sometimes puts a Dark Star in one of the chests. If the player pays Koopa Kid for this chest, they will be forced to take the Dark Star inside.

In Mario Party DS, they were renamed Ztars again, and occasionally appear in Hidden Blocks. If a player is unfortunate enough to get one, he/she will lose a star. Also a figure called Ztar appears at the same time the star figure appears.