Pyrovile
Pyrovile first appeared in The Fires of Pompeii (Series 4 : Episode 2) as large rock-based humanoid beings with a magma interior. The Pyrovile crashed on Earth when they escaped their own planet after it was stolen by Davros. The Pyrovile’s on board were destroyed in the crash, and they lay dormant in the core of Mount Vesuvius, eroding into dust particles. After an Earthquake in 62 A.D., they were woken up and their dust particles were inhaled by the humans in the nearby town of Pompeii. They were able to influence the Soothsayers of Pompeii to construct a ventilation system around the town, allowing the dust of the Pyrovile to be inhaled by all the inhabitants. The result of breathing in the dust of the Pyrovile turned humans into Pyrovile themselves, or heightened the psychic abilities of some of the Soothsayers, who were able to accurately predict the future from the time rift that formed around Pompeii.
The Pyrovile were able to shoot flames out of their mouths, turning humans to ashes in seconds. Their weakness was, naturally for fire based creatures, vast amounts of water, which snuffed out their internal body heat and they solidified. By 79 A.D., the Pyrovile had bodies again and had built a base underneath Mount Vesuvius, with the plan of converting the power of a volcanic eruption to change all the humans on Earth into Pyroviles. The Tenth Doctor stopped them from completing this plan by making Mount Vesuvius erupt, destroying the Pyroviles and Pompeii in the process.