The name 'Marxio Kart' is unofficial as it was not actually named in the comic.
The Marxio Kart has two forms. Its standard mode appears to be a triple-module hovercraft with one of the Marxios riding each module. The central module (Grouchio's) is adorned with a metallic clown face. When switched to combat mode, the vehicle transforms into a spherical combat mecha with two huge arms and a ridiculous assortment of heavy weapons. The clown face also frowns menacingly. The Marxio Kart's combat mode somewhat resembles Doctor Robotnik's Squeeze Tag Machine. The Marxio Bros. attempted to kill Knuckles the Echidna with this machine and nearly succeeded, but Knuckles managed to defeat it by burrowing underground and attacking from beneath it.
A similar vehicle was mentioned during The Battle For Mobius. The Marxio Cart is presumably a light racing cart adapted for battle and contains an assortment of weapons. Sab was ordered to send out her men to prep the cart, ready to fight off the Badnik army invading the Chemical Plant Zone. This version is a direct parody of the "Mario Kart" series.