Petey Piranha

Petey Piranha is a reoccuring villain in the Mario series. His first ever appearance was Super Mario Sunshine.

Super Mario Sunshine
In Super Mario Sunshine, Petey appears in two missions on Bianco Hills. The first mission he is in you have to squirt water in his mouth, causing him to swell so much that falls. When he falls his belly button will be sticking out and you must ground pound it. In the other mission you must squirt water in his mouth, waking him up. He will then fly around, and Mario must squirt water in his mouth so he falls and Mario then must ground pound him.

New Super Mario Bros
In New Super Mario Bros, Petey Piranha is the final boss of World 5. Mario defeats by ground pounding him. If Mini Mario defeats him World 7 unlocks.

Subspace Emissary
Petey Piranha is the first boss in the Subspace Emissary.