To defeat Dino Piranha, Mario or Luigi (depending on which mode is played) must hit its tail with a spin which would cause the tail to backlash and hit the back of its head. Dino Piranha would then lose some of its head petals and make it enraged. When enraged, the Dino Piranha will move faster. When enough damage is dealt, the Dino Piranha will explode.
Fiery Dino Piranha
Present in the Melty Molten Galaxy, a different version of Dino Piranha appears as the boss of the area. The Fiery Dino Piranha fights exactly the same as the regular Dino Piranha, with some changes to give its fiery approach: the tail occasionally bursts into flames, making it precise when to hit the tail to avoid being burnt. After the first hit, the Fiery Dino Piranha leaves behind a trail of fire from its footsteps, and then occasionally shoots out a fireball from its mouth after the second hit. After the final hit, the Fiery Dino Piranha explodes.
When Mario (or Luigi) arrives to the planet where Dino Piranha is standing, it is surrounded in a giant egg that Mario must spin at it's tail that has a rock on it to make it swing back and break the egg.
Once Dino Piranha is "freed", it tries to kill Mario and he must spin once again on the rock on it's tail to make it spin back and hit Dino Piranha, and do so for three times where each time it gets hit it becomes angrier and faster.
In the Boss Blitz Galaxy of Super Mario Galaxy 2, Dino Piranha is one of the five bosses (along with King Kaliente, Major Burrows, Bouldergeist, and Fiery Dino Piranha) to defeat in order to earn a star, and the first fought.
A similar boss in Super Mario Galaxy 2 called Peewee Piranha strongly resembles the Dino Piranha.