From the Super Mario Wiki, the Mario encyclopedia
In Mario Party 2, when used, the Plunder Chest randomly chooses another player that is holding an item, steals their item and gives it to the player. In Mario Party 3, players can choose who they want to steal from; however, if the person being targeted has two or three items, the item that is stolen is picked at random.
In Mario Party 2, the stolen item can be used on the same turn.
There is a much rarer version of the Plunder Chest in Mario Party 3, called the Barter Box, which swaps all of the player's items with all of the targeted player's items.
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