Puffstool

Quote from The Legend of Zelda: The Minish Cap Puffstool figurine: "Appears in Deepwood Shrine. These mushroom beasties scatter spores all over dungeons. When their caps are red, they are invincible."

Puffstool is a monster that is quite easy to defeat, although it often lies withing the sand that slows Link down. When you use the Gust Jar to it, it goes grey and with a small amount of sword slashes it should be done. Puffastools appear in a variety of places, often places like dungeons and caves.