Il Piantissimo

Il Piantissimo is a man disguised as a Pianta that the player must race in Super Mario Sunshine, similar to the Koopa the Quick races in Super Mario 64. He could be raced in Gelato Beach, Noki Bay, and Pianta Village.

Once the game is beaten with 119 Shine Sprites or less, the ending screen will show Il Piantissimo finding Bowser Jr.'s Magic Paintbrush. This alludes to the possibility that he took it. In Mario Golf: Toadstool Tour, Shadow Mario is playable. A likely possibility is that this is Il Piantissimo wearing the disguise, as Bowser Jr. is also playable in the game.

Trivia

 * Without his fake Pianta head he looks just like the running man from The Legend of Zelda: Ocarina of Time.
 * If Shadow Mario is idling, he will stand and jerk his head like Il Piantissimo.
 * Il Piantissimo may be in Super Mario Galaxy, where you can race 'Shadow Mario' (called Cosmic Mario) throughout areas. Il Piantissimo challenged you to races, so it is possible.