It manipulated the Brotherhood of Demnos into believing it was a god and eventually possessed the leader, Hieronymous, choosen 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.(DW: The Masque of Mandragora)
The Helix manifested in 1863 China, somehow free of the restraints based on star alignments, where an earlier Doctor confronted it without fully understanding it, as the Helix had encountered him in an earlier point in the timeline, yet a later point in the Doctor's personal timeline. (PDA: The Eleventh Tiger)
As the Fourth Doctor had earlier predicted, (DW: The Masque of Mandragora) 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. (DWM: The Mark of Mandragora) The Doctor and Ace had two other encounters with the Helix as well. (DWM: Darkness Falling, Distractions)
In May 2009, Mandragora reappeared in London, 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 throw it back into space, confused and with missing memory. (NSA: Beautiful Chaos)
Habits and Quirks
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.
The Helix seemed to exist as Mandragora energy and portions of this 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 absorbed through wire, with a ground like negative energy in magnetism.
The Helix could apparently travel through space but, in the case of Earth, could only reach the planet when the stars lined up in a certain orde. This opportunity came in five hundred year cycles. (DW: The Masque of Mandragora)
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. (NSA: Beautiful Chaos)
Inside the Helix was a black void where sound echoed and a series of concentric crystal rings stayed suspended, but there was a "ground" where beings could walk. Balls of helix energy, which looked like sparking, irregularly-shaped red blobs, might bounce around in this void. (DW: The Masque of Mandragora)