From the Super Mario Wiki
Mustached Hero! is a quest in Mario Party Advance that starts at the Spear Thicket. It can only be completed while playing as either Mario or Luigi; if Princess Peach or Yoshi visit the thicket, Spear Guy hops out of a bush and demands to challenge someone with a mustache before kicking the player out. Once the player makes it to the thicket as Mario or Luigi, Spear Guy hops out and proclaims that their mustaches is a sign of their bravery before challenging them to a duel (of the kind used by other duellists such as Chain Chomp during Chomper Stomper and Blooper during Blooper Battle). The player has the option of immediately running away, which leaves Spear Guy confused and sad, though the quest only begins if the player accepts the fight. Once the quest begins, Spear Guy specifically challenges them to the Tank-Down minigame, which involves fighting against another character while both are in control of a tank, and says that if the player wins, they get to keep the minigame. If the player loses (and does not use one of their Mushrooms to immediately retry the quest), Spear Guy is shocked that the player is weak despite their moustache, and forces them to retry the quest from the beginning. Once the player wins, Spear Guy graciously admits defeat and lets them keep the minigame. The quest ends once Spear Guy asks the player to come back later for a rematch (though attempting to revisit him only results in repeating the quest).
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