Mandragora Helix

The Mandragora Helix, also called the Mandragora constellation, (COMIC: The Mark of Mandragora) was a Helix Intelligence. A spiral of energy with a controlling intelligence, Mandragora existed as its own domain in "unchartered regions of the Time Vortex." (PROSE: Doctor Who and the Masque of Mandragora)

Origins
The Mandragora Helix originated in the Dark Times, the Tenth Doctor commenting that it should never have been freed from its dimension. (PROSE: Beautiful Chaos) Stranks, who confirmed he was part of the Helix, said it was old even when this universe was born, and that the sentient races of this universe had only encountered it in its dotage. (COMIC: The Mark of Mandragora)

Physical appearance
The Mandragora Helix was a spiral of pure energy that radiated outward, able to draw things into it, even a TARDIS. The function of the spiraling energy was a complete mystery. Inside the Helix was a black void where sound echoed and a series of five concentric crystal rings were suspended, but there was a "ground" where beings could walk. Balls of helix energy, which looked like sparking, irregularly-shaped red blobs, could fly through the void. (TV: The Masque of Mandragora)

Although it could be mistaken for a star in its corner of space, Mandragora was a superheated ball of psionic energy which acted as a containment protective field around its malign intelligence, (PROSE: Beautiful Chaos) although one account claimed there were several intelligences within the Mandragora Helix. (PROSE: Doctor Who and the Masque of Mandragora)

Powers
The Mandragora Helix was an intelligent astral force capable of speech. It had a powerful psychic force that could easily infiltrate human minds, yet might be repelled by the mind concentrating on something. Portions of Mandragora energy might be separated from the Helix and still act independently. Mandragora energy was the "subthermal recombination of ionised plasma" that could float through the air and burn anything it touched. With humans, contact resulted in instant death and a blue crystalline growth on the skin. This energy could be spread out over things like stone (recreating ruined structures) or living beings. In humans, the energy took over their bodies, giving them a white appearance that bleached out their faces but also allowed them to fire bolts of energy from their fingertips. With this energy spread out over stones or humans, it became exhausted more quickly. It could only acquire more energy at certain times. When in this exhausted state, it could be grounded through metal wire.

Mandragora was an astral force that based its powers on astrology, and while some people might not believe in it, this didn't stop Mandragora from using things like the Zodiac as power. (PROSE: Beautiful Chaos) Bound by the stars, the Mandragora constellation came into alignment with Earth every 500 years, requiring a bridge to reach the planet. If the mind was willing, the Helix was able to convert a human into a "Child of Mandragora," a humanoid pale/purple creature with roots that could kill. (COMIC: The Mark of Mandragora)

Pre-history
Mandragora had at least heard of the Time Lords and also knew of humans. It was worried that Man, if unchecked, would not be contained in his own galaxy, ultimately entering Mandragora's domain and becoming a rival in the universe. (TV: The Masque of Mandragora)



15th century
Having slipped inside the Doctor's TARDIS from its domain, the Helix travelled to late 15th century San Martino in Italy. It manipulated the Brotherhood of Demnos into believing it was the god they worshiped. It eventually possessed the leader, Hieronymous, chosen because he was the Duke's astronomer. Mandragora promised him he would be the Earth's supreme ruler. It took over the cult's members and planned to destroy several scientists who had been gathered so that Earth would be prevented from having the Renaissance. As the helix energy was exhausted, the Fourth Doctor was able to completely destroy it. (TV: The Masque of Mandragora)

19th century
A force believed to be the Helix manifested in 1863 China, by using a complex stellar event, where an earlier Doctor confronted it without fully understanding it, as the Helix had encountered him in a later point in history, yet an earlier point in the Doctor's personal timeline. At this point, it attempted to exert influence over China using previously 'recorded' copies of the minds of the first Emperor of China and his army, the information in the recordings edited to make the 'revived' emperor easier to control in his new body, but the Doctor and Barbara were able to convince the Emperor personality of the truth, giving him the strength to resist the Helix and destroy himself to protect his country. (PROSE: The Eleventh Tiger)

20th century
As the Fourth Doctor had earlier predicted, the Mandragora Helix re-appeared in 1990s London, this time exploiting the use of an illegal drug called Mandrake (another name for Mandragora). The Seventh Doctor and Ace, with the help of UNIT and Captain Muriel Frost in particular, put a stop to it. The Doctor and Ace had two other encounters with the Helix as well. (COMIC: The Mark of Mandragora, Darkness, Falling, Distractions)

21st century
Having sent out "sparks" to China and London to test the waters, Mandragora reappeared in London in May 2009, using the MorganTec computer systems company to spread its energy over the Internet. It decided that it was wrong about humans. Instead of stopping them, it would help them travel to the stars, acting as a leech all the while. The Tenth Doctor and Donna Noble, with help from Wilfred Mott, were able to disrupt its link to Earth by damaging the computer it was using to maintain its link to Earth, subsequently tricking it into possessing Wilf's friend Netty Goodheart. Taking advantage of Netty's Alzheimer's, The Doctor was able to weaken the Helix by forcing it to expend so much of its energy repairing Hetty's damaged synapses to allow it to think that it soon lost the ability to control her and was forced to retreat back into space, its mental energy already collapsing due to exposure to Netty's damaged mind. (PROSE: Beautiful Chaos)

Behind the scenes
Secrets of the Stars was originally going to use the Mandragora Helix. However, it was decided that "Mandragora had to change too much, and was too easily defeated, in order to fit this plot" and the Ancient Lights were created instead. Russell T Davies has said he likes to think both entities are "distant cousins". (DWMSE 23)