Tremblor

Tremblors, also known as Quake demons, were a race of rock-like demons with the power to generate localized earthquakes.

Physiology and powers
The Tremblors are composed of what appears to be rock, possess stalactite-like teeth, and have fully prehensile tails.

The Tremblors' primary power was the ability to generate powerful vibrations, allowing them to cause earthquakes and reduce organic beings to pulverized masses of flesh; Angel compared the effects of this ability to grabbing a bare electrical wire while having a heart attack. Additionally, they were superhumanly strong and incredibly resistant to physical damage. They were also telepathic, communicating as such and able to read the minds of others to some extent.

However, as a side effect of living underground, the typical Tremblor was extremely agoraphobic.

Reproduction
The Tremblors reproduced via human sacrifices involving four humans who work around the four classical elements (earth, water, fire, and air), such as firemen, lifeguards, gravekeepers, and flight attendants. Three of the typical humans were warriors, while the last one was typically passive and non-violent. The four sacrifices would be thrown into a lava pit, and emerge as a new Tremblor.