From the Super Mario Wiki
True-Blue Boo is a quest in Mario Party Advance that is given by Boo. It serves as the tutorial quest for Yoshi if the player starts the game as him, although it can be completed at any time by any character. Boo, along with a group of three other Boos, are concerned about an unspecified crime, and ask the player to solve it for them. They can either agree to help, which promptly starts the quest, or they can quickly refuse the offer, causing Boo to accuse them of being scared. Once the quest begins, Shroomlock arrives, and the Boos explain to him and the player that their Golden Boo Statue has gone missing. Shroomlock believes that it has been stolen, and the four Boos suddenly realize that there are four of them when there should normally be three. Shroomlock accuses the extra Boo of being the culprit, and asks the player to help him find the odd one out. The four Boos then start to move around in a dance-like pattern, with one of them occasionally breaking the pattern and moving in a different direction; this Boo is the culprit. If the incorrect Boo is chosen, the guilty Boo starts laughing (which isn't noticed by everyone else) and Shroomlock forces the player to restart the quest. Once the correct Boo is chosen, his transformation is removed to reveal that Koopa Kid stole the statue. He then sprints off, leaving the statue behind, and Shroomlock chases after him. To thank the player for their help, Boo gives them the Predictotron Gaddget.
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