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. The 6th level of World 3, The Cave of Harry Hedgehog, was named after this enemy and prominently features the hedgehogs. They usually appear in cave levels.

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

Trivia

 * Harry Hedgehogs may have been based on Porcupos from Super Mario Bros. 2 as indicated by their Japanese name.
 * Harry Hedgehog's coloration and rather quick moving pace may be a reference to another blue hedgehog in video gaming: Sonic the Hedgehog of the Sonic the Hedgehog series. 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.