Boshi is a blue Yoshi with an attitude. He was also the rival of Yoshi. Boshi is a loner who likes to wear sunglasses and a spiked collar around his neck. He (along with many other Yoshis) lives on Yo'ster Isle, home of the famous Mushroom Derby races.
One fateful day, Boshi defeats all the other Yoshis in a race and becomes the champion of the Mushroom Derby. Boshi then declares himself boss of the Yoshis. Under his reign, the races of the island are cancelled. In fact, the only one allowed to use the racetrack is Boshi himself. Although the other Yoshis disliked Boshi's rule, they felt obligated to obey the champion of the derby. But his reign ended when Mario and his friend Yoshi defeated Boshi in a race.