Prickly Piranha Plant & Relative

Prickly Piranha Plants are large, purple-headed, thorny-stemmed cousins of normal Piranha Plants found in Super Mario Galaxy. Being rooted to the spot, they remain stationary. But because they are covered in so many thorns, they cannot be silenced with a Star Spin. If you approach them, they will wind up and attempt to squash you by slamming their heads down in your direction. If you avoid this attack, you must stomp on its head before it gets back up. Thus it is defeated.

In Super Mario Galaxy 2, the Prickly Piranha Plant reappears along with a rare relative: the Spiky Piranha Plant.

Only one appears in the entire game. This relation is even trickier to defeat because its head is also spiny, rendering it unstompable. The only way to defeat it is to hit it with a Stretch Plant. It follows the same attack pattern as its relative. When defeated, it drops a key, which releases a Star from a nearby cage.