Mecha-Bowser

Mecha Bowser is a huge Bowser-shaped robot used by Bowser Jr. to attack Mario, and escape from him. In Super Mario Sunshine, Mecha Bowser was found in the first episode of Pinna Park, being controlled by Bowser Jr. To fight him, Mario must board a rollercoaster and fire Water Rockets (via F.L.U.D.D) at Mecha Bowser when he gets close enough. Mecha Bowser will attack by shooting Bullet Bills at Mario, and by breathing fire on the rollercoaster tracks. Eventually, Mecha Bowser is destroyed by Mario. Mecha Bowser also appeared in Mario Power Tennis. This lead players to assume that he was re-built by Bowser or Bowser Jr.. In this game he tilts the court. Later, in Mario Party 5, he is a giant toy that shoots characters out of a cannon. Also in Mario Party 7 his head apears in Bowser's Enchanted Inferno.

In Super Mario Galaxy, Mecha-Bowser appears in the Toy Time Galaxy; however, he appears very different from how he has appeared in the past games. In this game, instead of a robot, he is a toy robot and he doesn't look like Bowser a lot. This is probably because this Mecha Bowser is blue and green instead of the normal Bowser colors. To "defeat" Mecha Bowser, Mario must climb to the head of Mecha Bowser (similar to Megaleg) and then Ground Pound through the rocks on top and into its head to destroy it and free the Gearmos that were captured inside it. Note that this Mecha Bowser was called Heavy Metal Mecha Bowser instead. Another Mecha Bowser appears in Mario Party 5, in the Toy Dream board.

Trivia
A similar character called Bowser??? appears in Paper Mario. The False Bowsers and Bowser Clones of Super Mario Bros. and Super Mario RPG: Legend of the Seven Stars (respectively) could also be considered similar to Mecha Bowser, although they lack resemblance to him (looking identical to King Koopa himself rather than a cheap robot).