Helix Intelligence

Helix Intelligences were sentient astral forces that resided in/existed as spirals of pure energy. The only known Helix was the Mandragora Helix, (TV: The Masque of Mandragora) also called the Mandragora constellation, (COMIC: The Mark of Mandragora) though one account claimed there were multiple Intelligences within Mandragora. (PROSE: Doctor Who and the Masque of Mandragora)

Helixes possessed archetypal memories, able to absorb the emotions, consciousness, and genetic cells of others. (PROSE: Exodus Code) They had great manipulative power that could recreate stone structures or destroy beings, making their skin appear blue and crystallised. Their energies could be spread out, but this would exhaust their being, and their energy could become grounded by metal, rendering them harmless. (TV: The Masque of Mandragora)

The Tenth Doctor explained that Mandragora originated during the Dark Times, commenting that it should never have been released from its dimension, (PROSE: Beautiful Chaos) implying the Helixes originated from outside the universe, since Mandragora was "old even when this universe was born." (COMIC: The Mark of Mandragora) They existed everywhere in the galaxies before any life forms, and may have been responsible for the first life forms.

In the 1960s, a cadre of physicists, which some said were a cult that experimented with LSD too much, posited a theory that a "powerful sentient astral force" was caught in the Big Bang, part of the force breaking off and fusing with the centre of Earth while the solar system was forming. They believed the energy force gave Earth its organic nature and that all life evolved from the force and was protected by it.

Helixes were neutral, impassive energy forces, (PROSE: Exodus Code) having no need for human beings, although they could possess them and transform them. (TV: The Masque of Mandragora) The Greeks called the Helixes Titans, "the gods of the gods." (PROSE: Exodus Code)

Apart from the Helix trapped within the Earth, Mandragora manifested on the planet in the 15th century, (TV: The Masque of Mandragora) possibly 1863, (PROSE: The Eleventh Tiger) the 1990s, (COMIC: The Mark of Mandragora) and in 2009. (PROSE: Beautiful Chaos)

Helixes were bound by the alignment of stars, only having access to the universe at certain times, (TV: The Masque of Mandragora) similarly to the Great Old Ones who also existed in the previous universe. (PROSE: White Darkness)

Behind the scenes
The Mandragora Helix is presented in Masque as "non-physical," a place called the Helix containing a living intelligence called the Helix, and the Doctor makes reference to "Helix Intelligences" implying more than one, while the novelisation refers to multiple intelligences within the Mandragora Helix. It has never been explained if Mandragora is its own race or hive mind or entity, since no other Helix was referenced until Exodus Code, and even there Jack Harkness says his friend witnessed "the Helix splitting," implying the Helix trapped in the Earth is also Mandragora. So it is possible that the Helix Intelligences and Mandragora may very well be the same, as opposed to Mandragora being one of several Helixes.