From the Super Mario Wiki
Lava Piranha is an enormous Piranha Plant boss in Paper Mario who, as its name suggests, lives in pools of lava. Only a single Lava Piranha has been seen in any Mario games so far, but according to Goombario and Koopa Koot, there are more than one.
The Lava Piranha featured in Paper Mario is the ruler of Mt. Lavalava on Lavalava Island. It is found in a small lava pool where the other Piranha Plants report to him. Once Mario defeats it for good, it falls to the ground and sinks back into the lava.
Lava Piranha speaks in shouts and shrieks, blathering out insults at Mario when he confronts him for the fifth Star Spirit, Misstar, whom Bowser ordered the fiery Piranha Plant to guard. Its attacks are rather simple. Most of its attacking is done by his Lava Buds. When it attacks, it spits out an orb of fire at Mario that does five attack damage to Mario.
After Mario defeats Lava Piranha, it suddenly emerges from the lava and gets forty more HP. This time, Lava Piranha's head is on fire and its tongue is sticking out. If Sushie is Ultra-rank, her Tidal Wave ability makes this second phase easy, and possible to beat without taking any damage, as water and ice attacks stun it for two full turns.
It has a cameo appearance in the credits of Paper Mario, poking its head out from behind Lavalava Island, alternating with Raphael the Raven.
The Lava Piranha in Super Mario-Kun is encountered after Sushie destroys a Spiny Tromp. Mario and his partners attempt to attack it by using a Snowman Doll, but it results in Kooper getting crushed. The Lava Piranha then spews Lava Buds that attack Mario and his partners. Sushie then encases Mario in Water Block and squirts Lava Piranha. Mario walks out of the water block and shouts, distracting Sushie. Lava Piranha then burns and injures Sushie. Despite this, Sushie inflates Mario with water and pushes him to Lava Piranha. Mario bursts, spraying the water over Lava Piranha and thus defeating it.
Lava Piranha bears some resemblance to the boss Naval Piranha from Super Mario World 2: Yoshi's Island, except smaller and with fewer Piranha Buds and tentacles. Lava Piranha has a large tongue and white ring markings instead of filled white spots on its head, like typical Piranha Plants.
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