Carbuncle is a sand elemental. He was trapped under Tronin Desert for centuries until he was released by Azriel al-Zarar. He sensed Yurius's influence on Azriel and chose to assist him, using the opportunity to finally be free from his prison. He participated in the Battle of Vanna and helped hold the line against the Northern Horde until he was weakened enough that he returned to the High Plane.
While the Battle of Vanna was raging on, the Northern Horde was planning to breach the walls of Vanna with their huge siege tower Helepolis. Guided by a voice he thought as Tronin's, Azriel al-Zarar travelled into the ancient tunnels beneath the sand and located an earth elemental which had been trapped within a cave by various high-level magic spells. Channeling his newfound powers, Azriel set the elemental free and enlisted his aid to help defend Vanna. The elemental promised to help Vanna for a little while because he was indebted to Azriel for freeing him and because he recognized the power which was guiding Azriel.
The earth elemental could manipulate the ground and sand of the desert and suck even large siege towers such as the Helepolis into the sand. Like any elemental, he fared well against multiple armed foes who he saw as mere annoyances. However, he was vulnerable to water due to being made mostly of sand.