The Koopa Clown Car (sometimes spelled as the Koopa Klown Kar) is one of Bowser's methods of travel. It is the shape of a bowl, big enough to hold Bowser and one human, with a small propeller on the bottom that propels the whole thing up in the air. There are no obvious controls; Bowser seems to be able to control it (and call it from a distance) mentally. The body has a smiling clown face on it; why it's not a Bowser face or something scarier instead is unknown.
The Koopa Clown Car's earliest appearance was the final boss battle of Super Mario World, in which Mario had to defeat Bowser as he flew around the stage in the machine. It held Big Steelies and Mecha-Koopas to use as projectiles, as well as Bowser and the captive Princess Peach. The Clown Car appears in other games as a form of travel for Bowser, such as in Mario & Luigi: Superstar Saga. Recently, in New Super Mario Bros. Wii, Bowser Jr. has his own, smaller Koopa Clown Car and uses it to battle Mario, called Junior Clown Car. He also uses his father's Koopa Clown Car much later in the game.
The Koopa Clown Car appears as a normal trophy, collectable through either the Lottery or in Classic or Adventure Mode after you get all Classic, Adventure, All-Star trophies.
Bowser's single-seat, personal airship doesn't exactly handle like a dream, but it wasn't designed to be sporty. The Koopa Clown Car was made to carry Bowser's huge weight, not to mention a logic-defying arsenal of massive bowling balls. In Super Mario World, Mario busted the Koopa Clown Car by pelting it with Mecha Koopas.
- Super Mario World
Initial speculation theorized that the Koopa Clown Car would be Bowser's On-Screen Appearance in Brawl. However, it turned out that it was only used as a plot device in the Subspace Emissary, allowing Bowser to get out of tight spots without having to deal with any of the heroes. Unlike in Melee, there is no trophy of the Koopa Clown Car.
The Junior Clown Car is used Bowser Jr. and the Koopalings as part of their character. The Clown Car would show many capabilities taken from the Mario series, such as launching cannonballs and Mechakoopas, as well as using various tools such as wrecking balls, boxing gloves, buzzsaws, and a fork. The Junior Clown Car is also capable of licking opponents, sprouting wheels for driving, or transformed into an exploding projectile via abandoning it, though a new one respawns upon landing.
It should be noted that Bowser Jr. takes less damage while inside the Clown Car, which is essential to Bowser Jr's survivability.
The Junior Clown Car's design varies on its user: Bowser Jr.'s takes its design directly from Bowser's, while the Koopalings' Clown Car has yellow eyes and an orange mouth, and its color of the rim of the car as well as the propeller varies on the Koopaling (for example, Ludwig's is blue, while Lemmy's is yellow). The Junior Clown Car will also show facial expressions based on the current state of the user (angry when attacking, sad when being attacked).
The Junior Clown Car appears in Bowser Jr.'s on-screen appearance (where it flies in before the respective user pops out), as well as his victory poses.