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 is most useful in winter-themed levels, such as Cool, Cool Mountain and Snowman's Land. It can also kill any enemy on contact, making it very useful when there are enemies in the dinosaur's way.