Atrekna

The Atrekna are a precursor species that instigated the First Precursor War against both the Lanaktallan and Mantid. They are originally inhabited a parallel universe which was undergoing heat death, and found a way to access the universe of First Contact through the hyperatomic plane that became Hellspace. They were driven back by the Mantid and Lanaktallan, and reemerged during the Human-Lanaktallan War on Hesstla.

Description
Atrekna average 3 meters in height. They have dark purple skin covered in a layer of mucus, and wear iridescent robes into battle. Their heads are pointed, with large white eyes without pupils or irises, and large tentacles make up the lower third of their faces. Under the tentacles is a tubular mouth lined with spiral rows of sharp teeth for consuming brains. They have many fingered hands.

Atrekna seem to fight primarily with psychic powers, using their psychic abilities to fly on conjured disks around the battlefield.

Tentacles over a lamprey mouth, conical head, white eyes, long fingered hands, no apparent sex organs or secondary sex characteristics. One heart, one lung, short and obviously tailored digestive system. Approximately eight times the nerve bundles as a Terran of approximately the same size.

History
The Atrekna originated in a universe far smaller than the one inhabited by Terran Descent Humanity, and quickly became masters of temporal manipulation. With this technology, they were able to conquer their home universe, however the temporal technology caused an acceleration of entropy and lead to their home universe undergoing heat death far sooner than would be natural. To survive, the Atrekna were forced to retreat to the last remaining stars in their universe and artificially extend the stars' lifespan, creating extremely dim red giants. They created the Dwellerspawn as living ships and weapons to compensate for a lack of resources, as it was more efficient to grow materials than harvest by conventional means.

At some point over 100 million years ago, the Atrekna found a way to Humanity's home universe through Hellspace and made contact with the Lanaktallan and Mantid. The three Precursors formed an alliance and made a superstructure construction yard to create Niven Rings in order to harvest the resources of the Milky Way. At some point, the Atrekna launched a sneak attack on the Mantid and Lanaktallan, leading to the First Precursor War, in which Hellspace was created by the Lanaktallen to prevent Atrekna Dwellerspawn from coming through. After this, they returned to their home universe, biding their time until their reemergence.

They revealed themselves during the Human-Lanaktallan War on Hesstla, sending their version of Autonomous War Machines, which have some resemblance to the Dwellerspawn, to the planet and harvesting Hesstlan brains. There they clashed with Terran forces for subjective decades, looping the same few months hundreds of times to fight the Terran forces in a battle of attrition. During this battle, they "reset" Terran Descent Human brains to a state before they achieved spaceflight with their temporal abilities in an attempt to pacify their enemy. This inadvertently reawakened suppressed Terran psychic abilities and brought catastrophic damage to the SUDS system.

Trivia

 * The Atrekna are based off of Illithids from Dungeons & Dragons.