Metal Yoshi is fought three times in Yoshi's Island '17; after Grain Graveyard, before Aqua Airborne and at the end of Platinum Palace.
His boss theme is a remixed version of Metal Mario's theme in Super Smash Bros.
Metal Yoshi's Fruit Machine Factory
When Yoshi reaches the end of the level, he comes across Kamek and a mirror. Kamek blasts the mirror with some magic, transforming it into Metal Yoshi.