Fendahl

The Fendahl were gestalt organisms from the original fifth planet of the Sol system. They were composed of two parts, a Fendahl Core and the Fendahleen. The Fendahl posed a threat to all life, and when one Fendahl Core and twelve Fendahleen coexisted they had the power to destroy all life on a planet.

Biology
Thirteen physically separate organisms made up the Fendahl.

Fendahl Core
The skull of the Fendahl Core which transported itself to Earth resembled a human skull in every respect, but for a pentagram shape in the forehead, visible only by an x-ray. After her transformation into the Fendahl Core, Thea Ransome appeared as a golden-skinned, majestic being with gigantic, unblinking eyes. (DW: Image of the Fendahl)

Fendahleen
Each Fendahl Core had twelve Fendahleen, large eyeless and limbless creatures with a fringe of pink tentacles around and two large fins above their mouths. Table salt, which affected the electrical conductivity and osmotic control of their cells, was fatal to them. (DW: Image of the Fendahl)


 * It is unclear if the Fendahl Core had the same vulnerability.

Life cycle
Fendahls were psychevores, meaning they fed on psychic energy. (NA: The Left-Handed Hummingbird) The Fendahl could drain all the spectrum of energy from their prey, effectively sucking out their souls. Even the skull nicknamed Eustace, the fossil remnants of a Fendahl Core twelve million years dead, had the power to drain the life force of the Fourth Doctor. The Core could create these Fendahleens from living beings with the correct genetic inheritance and in some cases could create the Fendahleen out of pure energy.

If the Core was destroyed, the Fendahl was killed. All of the parts of the Fendahl could telekinetically control people, but the Core had many more psychic powers such as mind control and astral projection. (DW: Image of the Fendahl)

History
Roughly 12 million years BC, the Fendahl evolved on the Fifth Planet, located between Mars and Jupiter. The Fendahl began to kill all life on the planet, including each other. When the Time Lords learnt of the danger that the Fendahl posed, they placed the planet in a time loop. They also removed all trace of the Fendahl from their records, leading it to pass into legend.



However, a Fendahl survived and was able to escape the planet in the form of a skull. (DW: Image of the Fendahl) In its travels it caused damage to Mars, leading to mass extinction. (DW: Image of the Fendahl, NA: GodEngine) It eventually came to Earth, arriving in Kenya. This skull was able to affect the development of humans in order to produce a species which it could use. (DW: Image of the Fendahl)

In 1098, a Fendahl somehow came to Jerusalem, attracted to the destruction caused by the Crusades. (THN: Deus Le Volt)

The skull was eventually discovered by Dr. Fendleman in the 1960s by discovering a "sonic shadow" and tracing it back to its source. He brought it back to Fetch Priory, which had a time scanner. The Fendahl was able to grow in power using the time scanner, killing several people and possessing Thea Ransome. A local coven, led by Maximillian Stael, believed they could control the Fendahl and tried to help it, but were instead turned into Fendahleen. The Fourth Doctor was able to stop the Fendahl by overloading the time scanner and removing the skull, planning to dump it in a supernova. (DW: Image of the Fendahl)

This act, however, failed to destroy the Fendahl. Instead, it wound up causing another manifestation of the Fendahl on Kaldor City. (Kaldor City: Checkmate)

During the War with the Enemy, Time Lords from the Eighth Doctor's subjective future had planned to use a fleet of War TARDISes to undo the time barriers around Planet 5 in order to release the Fendahl, but it was discovered that the Fendahl had been killed when time inside the loop was accelerated, resulting in the last other life-form on Planet 5 evolving into the Maemeovore, a devourer of concept that had evolved to kill the Fendahl itself. (EDA: The Taking of Planet 5)