From the Super Mario Wiki
Il Piantissimo is a human disguised as a Pianta that the player must race in Super Mario Sunshine, similar to Koopa the Quick races in Super Mario 64. He can be raced in the 5th levels of Gelato Beach and Noki Bay, and in the second level of Pianta Village. Il Piantissimo's name could be a portmanteau of the words "Pianta", whom he is dressed as, and "Pianissimo," which is Italian for "very soft", usually used in musical notations, though it is worth noting that "-issimo" itself is an Italian suffix for "extremely."
Piantissimo is very overconfident, and finds himself much superior to others. According to various locals at Pianta Village, he is considered a rogue, a creep, and not related to the Piantas. This could show that due to his attitude, he is left alone and barely challenged, fueling his ego as there is no one to compete against him.
When Mario races against Il Piantissimo, the two must head to a flag that represents the finish line. If Mario wins, he gets a Shine Sprite, then completing the mission. However, Mario loses a life if Il Piantissimo finishes first. Also, if the player replays a completed Il Piantissimo episode, Il Piantissimo is more difficult to beat, as he finishes the course with the player's previous time. However, Il Piantissimo cannot use any tactics involving F.L.U.D.D.
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