Koopa Clown Car
The Koopa Clown Car is Bowser's favored mode of transportation. It is a helicopter-like vehicle with a large clown face painted on the side. He uses it in Super Mario World, Super Mario RPG: Legend of the Seven Stars, Paper Mario, Mario Golf: Toadstool Tour and Paper Mario: The Thousand-Year Door. He also uses it in Mario Party 7, and Bowletta uses it in Mario & Luigi: Superstar Saga. In Paper Mario a massive stone one was built to support Bowser's Castle as it lifted up Peach's Castle.
The Koopa Clown Car appeared once in the Super Mario World cartoon series in an episode named (fittingly) Send in the Clown.
Some people think there may be a Warp Pipe in the Clown Car because Bowser can somehow fit himself, the Princess, Mecha-Koopas, Super Mushrooms and Big Steelys the size of the Car itself in it.
In Mario Kart DS Bowser drives a plane that looks like the Clown Copter/Koopa Clown Car.
The Koopa Clown Car also has its own trophy in Super Smash Bros. Melee.
