Peewee Piranha is the first boss in Super Mario Galaxy 2. It is found in the Sky Station Galaxy, on the Geo planet, and is fought in Mission 1: Peewee Piranha's Temper Tantrum and again in the Speedy Comet Mission: Peewee Piranha's Speed Run. Peewee Piranha also shares a close characteristic with Dino Piranha, but the differences are that he keeps his egg on, and doesn't have a tail.
After making his way to the Geo Planet where the boss makes his home, Mario inadvertently breaks Peewee Piranha's egg. This angers Peewee and causes him to break out of the egg.
Peewee Piranha will chase Mario and jump at him with his mouth. Mario must use his Star Spin to strike the back of the boss three times in order to expose the tail. After Mario damages him there again, Peewee Piranha will suffer his REAL tantrum and enter Phase 2, turning red with rage.
During Phase 2, Peewee will chase Mario more aggressively, with longer and more numerous strides before resting for a few seconds. When it is hit for the fifth time, it will run away faster than Mario can run. Peewee Piranha must be intercepted, where it will stop for a quick moment to turn around, so the final hit can be dealt on his "tail".
At the end of the battle, Peewee will collapse without any petals on his head (which turns blue to show Mario defeated him), and he will finally explode to reveal the Power Star.
Peewee retains his strategy in the Speedy Comet mission, but the player has an extreme time crunch, so Peewee's planet has timers to buy time.
- Like Dino Piranha from the first Super Mario Galaxy, Peewee Piranha resembles Petey Piranha, with one particular feature that he doesn't have (in his case, the eggshell) that must be attacked. Also, all three are the first boss of their respective games and two of the three are first encountered enclosed in an egg. They are also battled as the first boss of their games and two of them once again under Speedy Comet conditions. They are also both in the first levels of the first galaxy in their games (not counting Gateway Galaxy).
- The non-English names suggest that it is seemingly the child of Dino Piranha. Additionally, some fans claim that Peewee Piranha is Dino Piranha's cousin.
- Peewee's name derives from the word "pee-wee", which is a word that can be used to describe something small or immature, which Peewee Piranha obviously is, and may have also derived from Petey Piranha.
- Every time Peewee Piranha generally does anything, a squeaking noise can be heard.
- Peewee Piranha shares his boss theme with Sorbetti, Rollodillo, and Prince Pikante. This implies that that may be the main boss theme for the game.
- Peewee Piranha's boss theme was also placeholder music for Boom Boom's boss battle in the Super Mario 3D Land demo.
- Peewee Piranha's boss planet is surprisingly host to Dino Piranha in Mario & Sonic at the London 2012 Olympic Games during Dream Spacewalk.