Fucanglong is the Chinese underworld dragon which guard buried treasures, both natural and man-made. Volcanoes are said to be created when they burst out of the ground to report to heaven. Fucanglong is also known to possess a magic pearl which is his most treasured possession.
The pearl's capabilities itself are unknown, but for it to be guarded and kept so heavily by a dragon, its value and power must be above the likes of any gold and silver that a dragon would normally guard or keep to themselves.
Fucanglong himself is not necessarily malevolent, but due to his status as a dragon of the underworld he normally comes off as a cruel and highly apathetic dragon. However, this does not hinder his ability to perform his sworn duty. And that is to guard buried treasures and as well as keep the underworld stable.