Grunchin

A Grunchin (plural, "Grunchin") is an explosive sea urchin creature in Wario Land: Shake It!, being the only enemy to appear in both underwater Subwarine levels and standard platforming levels. In underwater levels, Grunchin form rings to barricade paths and block against the Subwarine's torpedoes. The rings are primarily made from invincible purple Grunchin, with red ones spread out between them. Only the red Grunchin can be destroyed, which in turn destroy all other Grunchin in the ring. The destroyed Grunchin produces a silver coin and a bronze coin for every subsequent Grunchin in its ring.

In other levels, such as Savannah Valley and Its-all Mine, red Grunchin are produced by spawners as timed hazards for the player to avoid and pass. Though they explode on contact with surfaces, it seems only the Grunchin itself can actually hurt Wario. As the torpedo is the only way to destroy a Grunchin, they are impossible to defeat in these levels.