From the Super Mario Wiki
Boo's Crystal Ball is an item featured in Mario Party 4. A player can use the item to summon a Boo to steal Coins or a star from an opponent. A Boo's Crystal Ball can be purchased at item shops or won in Mini Minigames. The player can stop the Boo from stealing coins by merely tapping rapidly, but this fails to deter Boo from stealing coins (unless they have a Gaddlight that scares the Boo away). The option to repeatedly tap is absent if Boo is stealing a Star. Players can also access Boo's Crystal Balls by visiting various Boo Houses on boards; there is a maximum of one Boo House per board.
Donkey Kong about to have his star stolen from the Boo.
Wario about to have his coins stolen via Boo House.
Names in other languages
Teresa no suishou
||Boo-Boule de Cristal