Shadow Mario

"Yaaaaargh! You're so annoying!"

- Shadow Mario

Shadow Mario is an evil doppelgänger of Mario and the main villain of Super Mario Sunshine. He has the same appearance of Mario, except that his body is blue and water-like, and his eyes are red. He also has an unusually long, red tongue. Shadow Mario wields the Magic Paintbrush, an invention created by Professor E. Gadd. Using the brush, Shadow Mario can create toxic Goop and even some enemies. Midway through the game, it is revealed that Shadow Mario was Bowser's eighth child, Bowser Jr., in disguise. Using a bandanna with an image of Mario's mustache on it, Bowser Jr. could make him self look like Mario. It is unknown how Bowser Jr. acquired the paintbrush. However, it is suggested that Professor E. Gadd gave the brush to him.

Super Mario Sunshine
At the beginning of Super Mario Sunshine, Mario, Princess Peach and Toadsworth travel to the island resort of Isle Delfino to get some much needed rest and relaxation. However, when they arrive, they discover the island has been covered in toxic graffiti. Worse yet, Mario is arrested by the Pianta police. During his trial, Mario was found guilty of vandalizing the island, causing the Shine Sprites to lose their power. However, the real criminal was Shadow Mario. Since they looked so alike (at least, to the Piantas), Mario was arrested instead of the doppelgänger. After being found guilty, Mario is ordered to clean up the graffiti. Until he does so, he is forbidden to leave the island. Shortly after the trial, Shadow Mario appears and kidnaps Princess Peach. Mario chases him, shooting water from F.L.U.D.D, and rescues the Princess. However, Shadow Mario escapes before he can be caught. Eventually, when Mario is on another part of the island, Shadow Mario returns and kidnaps the princess a second time. Shadow Mario takes Peach to Pinna Park. When Mario hears that the princess has been kidnapped, he immediately heads to the amusement park. Once there, Shadow Mario enters the cockpit of the gigantic Mecha Bowser, and begins to attack the plumber hero. After a long battle, Mario defeats the robotic creation. Shadow Mario then opens the cockpit and reveals his true form, Bowser Jr. The young Koopa then reveals that his father, Bowser, told him that his mother was Peach and that she had been kidnapped by the "evil" Mario. Thus, Bowser Jr. decided to frame Mario to punish him in order to save his "mother". That being said, Bowser Jr. activates his hot air balloon and takes Princess Peach to Corona Mountain, where his father awaits his arrival.

Shadow Mario periodically returns to the island to cause trouble for the real Mario. In fact, Mario must battle Shadow Mario in every world of Isle Delfino, and fights him several times at Delfino Plaza. To defeat him, Mario must shoot water from F.L.U.D.D at an escaping Shadow Mario. Once defeated, Shadow Mario will usually give up a Shine Sprite. In battles taking place in Delfino Plaza, Shadow Mario will carry a Yoshi Egg, used to hatch Yoshi, or one of F.L.U.D.D's nozzles. Defeating Shadow Mario in Delfino Plaza will unlock F.L.U.D.D.'s alternate nozzles and the use of Yoshi in Delfino Plaza. After he and his father are defeated, Bowser Jr. loses the Magic Paintbrush, preventing him from assuming his identity as Shadow Mario. However, the runner Il Piantissimo discovers the brush on the sands of Gelato Beach. It is unknown what Il Piantissimo does with the paintbrush, or if he even picks it up.

Mario Golf: Toadstool Tour
Shadow Mario is an unlockable character in Mario Golf: Toadstool Tour. However, Bowser Jr. is also a playable character. It is unknown if this Shadow Mario is an alternate version of Bowser Jr. or if it is someone else in disguise. This Shadow Mario is quite possibly Il Piantissimo, as in Toadstool Tour, he appears very energetic and acrobatic, similar to Il Piantissimo in Sunshine, where he was a professional sprinter.

Trivia

 * It is unknown who invented/created the mask that Bowser Jr. puts on and takes off to disguise himself as Shadow Mario (as seen upon beating Mecha Bowser).
 * Both Doopliss and Shadoo, from Paper Mario: The Thousand-Year Door and Super Paper Mario, respectively, can assume Shadow Mario-esque forms, though purple and black in color.
 * A character called Cosmic Mario (and Luigi's counterpart, Cosmic Luigi) appears in Super Mario Galaxy, and looks very similar to Shadow Mario. In addition, the music that plays when Mario races Cosmic Mario is very similar to Shadow Mario's theme music.
 * Shadow Mario appears as a sticker and in a poster on the Delfino Plaza stage in Super Smash Bros. Brawl.
 * There is a grand total of eleven Shadow Mario chases in Super Mario Sunshine; one for each seventh episode of each of the seven major courses, and four times in Delfino Plaza.