From the Super Mario Wiki
Blooper is a character in Mario Party Advance. According to his description, he trains regularly at the Mushroom Beacon to become a master duelist. When first encountered at the Beacon, he explains the concept of dueling and duelists, saying that he's training to become a duelist himself. He then asks for a quick duel. If his request is accepted, he's glad that he doesn't have to train alone anymore. He challenges the player to Hammergeddon, saying that they'll win the minigame if they beat him. If they succeed, he mopes because of his loss, but honors his deal. He also talks about how the best duelists are found in the Duel Tower before asking the player to return, saying that he'll be stronger.
Later, at Sushi Cliff, Blooper is one of the suspects in the case of who dragged Shroomlock off the cliff and to the ocean. He was one of the witnesses who saw Shroomlock get pulled in, along with Dolphin and Cheep Cheep. When he was interviewed by Sushi, he claimed to be an innocent "swimmer-by", crossing his tentacles as he said so. He turns out to be the one who pulled Shroomlock, since he was the only one who was actually able to pull Shroomlock. He then proceeds to apologize profusely before dashing off. The ending credits state that, to this day, Blooper continues to train and grow stronger.
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