Peewee Piranha is similar in appearance to the Dino Piranha, expect it is smaller and has only partially come out of it's egg, it's head and feet being the only parts visible. It also conceals a large, red behind inside it's egg, which is it's weak point.
When Mario lands on Peewee Piranha's planet, he lands on top of it's still unhatched egg, breaking it open and revealing Peewee's head and feet. It then begins to attack Mario by charging at him, just like Dino Piranha did in the first Super Mario Galaxy, but it also has an original attack where it will try to jump on Mario and crush him under it's weight. To deal damage to it, Mario has to use two Star Spin attacks to break it's egg completely, and then do another Star Spin on it's now exposed behind. Alternately, he could also do a Ground Pound on the egg to shatter it in one hit. After that, it will somehow regenerate it's egg and get angry, charging at Mario faster and using it's jump attack twice. Mario must smash it's shell again and spin into it's behind one more time to defeat it and receive a Power Star.
Peewee Piranha appears again later on in a level with a Speedy Prankster Comet; Mario must repeat the majority of the level, including the fight against Peewee, with a time limit. Peewee's tactics do not change at all in the rematch, the only difference being that there now clocks on the planet to refill the timer.