From the Super Mario Wiki
Sluggies are hairy slug-like enemies found in Super Mario World 2: Yoshi's Island and the remake Yoshi's Island: Super Mario Advance 3. They come in three colors: green, red, and blue. Sluggies can fall on Yoshi from the ceilings. Sluggy the Unshaven is the boss form of a Sluggy. The only place they appear in is Sluggy the Unshaven's Fort. They can be defeated by jumping on them.