From the Super Mario Wiki
Among their attacks is trying to fall on one of the heroes. They first rotate several times in place, and then teleport above one of the bros. before falling; if it was right side up before teleporting, it falls on Mario; if it will fall on Luigi, it will be upside down right before it warps up. If countered, it can fall several times (on the same target), and each time it is countered with a hammer, it takes damage.
They can also shoot lasers at Mario and Luigi. If the Piranha Planet shoots upwards, it either shoots at Mario or shoot from Mario to Luigi. If it shoots upside down, it either shoots Luigi or shoots from Luigi to Mario. If it shoots at one person, it does it multiple times.
Its last move is to spawn many Piranha Plants and shoot them at a brother. The mini astronaut Piranha Plants pop out of its holes one at a time, coming in two different colors: orange for Mario and green for Luigi. The planet starts spinning, and slightly less than two seconds later, the Piranha Plants fly off the planet towards the bros. in the same order in which they appeared on the planet.
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