From the Super Mario Wiki
Mostosti Vomitonus is an enemy class in Super Mario World 2: Yoshi's Island and Yoshi's Island: Super Mario Advance 3. Its name is a pseudo-scientific corruption of "Most toasty vomit on us". Enemies in this class can be eaten and give a Yoshi the ability to breathe fire. The only members in this group are Flamer Guys and Lava Bubbles.