Fire Power (Yoshi)
From the Super Mario Wiki
“Yoshi has a bad case of heartburn from gobbling enemies. With the Power Flower, he can breathe fire! Try it out in Standard Mode by pressing ! I've heard barbecued Goomba is a delicacy.”
Fire Power is Yoshi's Power Flower power-up in Super Mario 64 DS. Getting a Power Flower or eating fire will allow Yoshi to breathe fire, though only the former lets him do so as much as he wants for a brief time.
The power-up itself has the most use in ice courses such as Cool, Cool Mountain and Snowman's Land, due to its ability to melt Ice Blocks. It can also defeat any enemy on contact, making it very useful when there are enemies in Yoshi's way.