|First game||Super Mario RPG: Legend of the Seven Stars|
Boshi is a Yoshi who only appeared in the game Super Mario RPG: Legend of the Seven Stars for the SNES. This Yoshi has a bad attitude, and you can pick it out from the others by his sun-glasses, chain around his neck, and the fact that he doesn't wear shoes like the other Yoshies do. Before Mario came to Yoshi's Island, Boshi was the best racer in the races titled Mushroom Derby on the island. Once he won all the other Yoshies on the island, he declared himself king of the Yoshies, and allowed no one else except him to race on the derby.
Once Mario came to the island, the main green colored Yoshi told Mario about Boshi. So Mario then told Yoshi that he would help him beat Boshi. So Yoshi told Boshi that if he'd win, they would give him Yoshi Cookies (Cameo of the Game), Boshi's favorite food. Boshi accepted and Yoshi plus Mario got to race Boshi.
If Mario and Yoshi won, he'd be the new champion. When the other Yoshiies decided to declare him the boss of the Mushroom Derby, he declined and said that its free to everyone including Boshi, who later learned his lesson.
Boshi is considered to most people as Yoshi's own Wario. Even in Japan, Boshi's name is Warshi, which the first three letters are Wario's. So in conclusion, Mario's evil twin is Wario, Luigi's is Waluigi, and Yoshi's is Boshi, or Warshi, according to most fans.