Harry Hedgehog

Harry Hedgehogs are small, quick-moving blue hedgehogs that appear in Super Mario World 2: Yoshi's Island and its remake Yoshi's Island: Super Mario Advance 3. If Yoshi gets too close to one, the hedgehog swells to a huge size, its spines sticking out. They cannot be eaten while in their defensive position. They usually appear in cavern levels; the 6th level of World 3, The Cave of Harry Hedgehog, is named after this enemy, and prominently features the hedgehogs.

They appear in another level in Yoshi's Island: Super Mario Advance 3, in Go! Go! Morphing!.

Harry Hedgehogs reappear in Yoshi's New Island for the Nintendo 3DS, and their spines are now purple instead of blue. They prominently appear in Harry Hedgehog's Labyrinth.

Trivia

 * Harry Hedgehogs may have been based on Porcupos from Super Mario Bros. 2, as indicated by their Japanese name.
 * Harry Hedgehogs are almost undoubtably a reference to Sonic the Hedgehog, since they are blue and move very fast. During the 16-bit era (which happened to be the time that Super Mario World 2: Yoshi's Island was released), Sonic's company of origin, Sega, often mocked the works of Nintendo in various ways (as Nintendo and Sega were business rivals). The Harry Hedgehog may be a retaliation to these mockeries, which may also explain its change in color for its latest appearance.