From the Super Mario Wiki
Blooper Battle is a quest in Mario Party Advance given by Blooper. It starts when the player enters Mushroom Beacon and accepts Blooper's duel. Declining makes Blooper sad, since he is completely alone and has nobody to train with. After accepting the duel, Blooper mentions that he is nervous about the match before offering a reward to the player if they win the duel. The duel is a minigame, Hammergeddon, with the winner being whoever can beat the opposing player with hammers first. If Blooper wins (and the player does not restart the minigame using a Mushroom), Blooper is elated about his first victory and offers to let the player try again, which involves restarting the whole quest. If the player wins, Blooper compliments the player's duelling skill and gives them the Hammergeddon minigame as a reward.