Zombone

Zombone is the skeletal counterpart and second form of the Czar Dragon. When Czar Dragon is hit a lot of times, it falls in the lava, loses its skin, and becomes its other form, Zombone. Zombone does a lot of dangerous attacks to Mario, Peach, and Bowser, such as sending out boulders to attack the three of them or headbutting into them using its big skull. After the gang hits Zombone enough times, Zombone explodes and collapses into the lava, defeated.

While Zombone has stronger attacks than the Czar Dragon, it has less defense. It is also vulnerable to thunder attacks. It no longer has the power to use fire attacks or summon Helios.

Trivia

 * Czar Dragon's death and rebirth as Zombone is similar to Bowser's death and return as Dry Bowser in New Super Mario Bros.
 * Its name is a portmanteau of "zombie" and "bone".
 * It highly resembles the Bone Dragon, Bonetail, and Bonechill.
 * "Zombone" was also the name of an enemy in the game Final Fantasy VI for the SNES, also developed by Square. Interestingly, the game's coding also contains a deleted superboss named "Czar Dragon."