From the Super Mario Wiki
Zombone is the skeletal counterpart and second form of the Czar Dragon. When Czar Dragon is damaged enough, it falls in the lava, loses its skin, and becomes its other form, Zombone. Zombone has plenty of dangerous attacks, such as sending out boulders to attack Mario, Peach, Mallow, Geno, and Bowser, or headbutting them. After the gang defeats Zombone, Zombone explodes and collapses into the lava, never to be seen again.
While Zombone has stronger attacks than the Czar Dragon, it has less defense and a weakness to thunder attacks. It also loses the power to use fire attacks or summon Helios. Being also an undead enemy, Zombone is vulnerable to the Pure Water item. However, Pure Water only causes a fixed damage of 200 points to Zombone instead of defeating the enemy entirely, like other non-boss undeads.
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