Koopa Clown Car
The Koopa Clown Car appears as a normal trophy, randomly obtainable after getting at least 250 other 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.
The Koopa Clown Car's only appearances are in the Bowser Kidnaps Peach/Zelda cutscene in the Subspace Emissary mode, in which Bowser, having stolen a trophified Peach/Zelda, uses it to escape from the heroes. It also appears in the Falco Appears cutscene.
The main version of the Koopa Clown Car featured in Super Smash Bros. 4 and Super Smash Bros. Ultimate is Bowser Jr.'s personal Junior Clown Car, which he rides in battle. The Koopalings, which appear as Bowser Jr. alternate costumes, use a different, mass-produced model.
As a fighter ability
Bowser Jr. and the Koopalings take 0.88× of the damage an attack would usually deal if the Junior Clown Car is hit. However, if their body is hit, they take 1.15× of the usual damage instead.
The Koopa Clown Car first appeared in the final boss battle of Super Mario World, in which Bowser rides it across the arena. It holds a seemingly infinite supply of Big Steelies and Mechakoopas for Bowser to attack Mario with, and in the last phase of the battle it directly attempts to crush Mario. Princess Peach is also kept prisoner in it and during the battle occasionally aids Mario by throwing Super Mushrooms at him.
The Clown Car made several reappearances in later games as one of Bowser's main means of transportation, often during cutscenes. New Super Mario Bros. Wii introduced Bowser Jr.'s own, smaller Koopa Clown Car, the Junior Clown Car, which he uses to battle Mario; he also uses his father's Koopa Clown Car much later in the game. The Koopalings ride the original Koopa Clown Car all together in New Super Mario Bros. 2. Super Mario Maker included the Koopa Clown Car as a level element, which can be ridden by Bowser, Bowser Jr., other enemies, and even Mario himself.