Boo's Crystal Ball

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 (for 5 coins) or a Star (for 50 coins) 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 when he runs after their coins and stars). However, they can press and can lose less coins. Up to 30 coins can be stolen from the opponent. The option to repeatedly tap is absent if Boo is stealing a Star (but not absent if the player uses a Gaddlight). Players can also access Boo's Crystal Balls by visiting Boo Houses on boards; there is a maximum of one Boo House per board.

The Boo's Crystal Ball has the same gameplay effects as the Boo Bell from Mario Party 2 and Mario Party 3, but provides a more "realistic" view of the Boo attacking the targeted player, as opposed to the Boo attacking the targeted player's status panel as before.