Peewee Piranha first appears enclosed in an Egg, similar to Dino Piranha and Fiery Dino Piranha in the first game, on the Geo Planet. When Mario lands on the planet, he lands on top of the egg, cracking it open and releasing Peewee's head and legs. Peewee immediately begins attacking Mario by charging right at him, much like its predecessor, but it also has its own original attack, jumping up into the air and attempting to crush Mario beneath its weight. After Mario has hit Peewee once, it will jump at him twice.
To defeat Peewee, Mario must hit it in its only weak point, its glowing red behind. However the behind is protected by the shell of the egg. To get rid of the shell Mario has to spin it three times which will prompt it to shatter off of Peewee's body. Mario can also Ground Pound the top of the shell to instantly shatter it completely. The Piranha Plant's enormous bottom is then open to attack. After Mario hits it once, Peewee will get mad and its head will turn red, just like another Piranha Plant. Its shell will also reform and its charges will speed up. Mario must repeat the process of destroying the shell to hit its behind and win the battle, gaining a Power Star.
Peewee Piranha later appears in a level with a Prankster Comet; a Speedy Comet. Mario must repeat most of the level, including defeating Peewee, with a timer. Peewee does not change its tactics for the rematch with Mario and continues to just charge and jump at him. The only difference is that the planet is covered with clocks to refill the timer.
Notably, whenever Peewee Piranha does generally anything, a squeaking noise can be heard.