The Blue Ox Kart is supposed to resemble the blue Ox from the tale of Paul Bunyan. You can get it from a secret code that CC gave out in her last blog post of 2017. Although the Blue Ox Kart was new, it used the same base as the Longhorn Kart. The Blue Ox Kart is very popular.
To get the blue ox kart put in the secret code PAULBUNYAN