Peewee Piranha is similar in appearance to the Dino Piranha, except she is smaller and has only partially come out of her egg, her head and feet being the only parts visible. She also conceals a large, red behind inside her egg, which is her weak point.
When Mario lands on Peewee Piranha's planet, he lands on top of her still unhatched egg, breaking it open and revealing Peewee's head and feet. She then begins to attack Mario by charging at him, just like Dino Piranha did in the first Super Mario Galaxy, but she also has an original attack where she will try to jump on Mario and crush him under her weight. To deal damage to her, Mario has to use two Star Spin attacks to break her egg completely, and then do another Star Spin on her now exposed behind. Alternately, he could also do a Ground Pound on the egg to shatter it in one hit. After that, she will somehow regenerate her egg and get angry, charging at Mario faster and using her jump attack twice. Mario must smash her shell again and spin into her behind one more time to defeat her 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 are now clocks on the planet to refill the timer.