Mecha-Bowser

Mecha Bowser is a huge Bowser-shaped robot first used by Bowser Jr. to attack Mario and escape from him in Super Mario Sunshine, but it has since made several appearances in some form or another in other games, including another main series title and various spin-offs. It may have been created to "rule" over Mecha-Koopa robots, as implied by its name, but this is not confirmed.

Super Mario Sunshine
Mecha Bowser is found in the first episode of Pinna Park and is piloted by Bowser Jr. To fight it, 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. After enough hits, the mech will explode, and Bowser Jr. will use its head to escape.

Super Mario Galaxy
Mecha Bowser appears in the Toy Time Galaxy; however, its appearance has been drastically altered from that in previous games. It is now a toy robot and, out of all of Mecha Bowser's incarnations, resembles Bowser the least. It also sports a blue and green color scheme. To "defeat" Mecha Bowser, Mario must climb on its head, dismantling portions on his way, and then Ground Pound through the rocks on top to cause the robot to explode and free the Gearmos inside it.

Mario Golf series
While Mecha Bowser does not physically appear in the series, its name appears on scoreboards in Mario Golf: Toadstool Tour and Mario Golf: Advance Tour.

Mario Power Tennis
In Mario Power Tennis and its Wii port, Mecha Bowser is the boss of the Mecha-Bowser Mayhem minigame, in which it tilts the court and battles players, firing Bullet Bills and Bob-ombs that can be deflected back at it. Players must attack it with charged tennis balls until its rampage is quelled.

Mario Party series
In Mario Party 5, Mecha Bowser is a giant toy on the Toy Dream board and shoots characters out of a cannon in its mouth to another location on the board whenever they land on a nearby ? Space. In Mario Party 7, its head is a feature of Bowser's Enchanted Inferno!. In Mario Party 9, its head is featured on the Bowser Station board as a Jackpot Machine. It stores Mini Stars, and players can earn these stars by playing minigames or by landing on Jackpot+ Spaces.