From Halopedia, the Halo wiki
Favor of the Librarian
While preparing her plans for Bastion, the Librarian had a structure built on Erebus VII in which the Precept would administer a final test and reveal the location of the shield world to those worthy. The Lifeshaper favored the Eiyaa-Mahtuhaa, making them a hurdle to overcome as part of this test. Evidently, she ensured that this species would be reseeded on Erebus VII after the firing of the Halo Array.
Study by humanity
Sometime after the United Nations Space Command discovered Erebus VII, ONI sent various teams of scientists to the surface and established at least five research bases to study the planet, its wildlife, and anything else that could be found. The researchers came across a nest of very young juvenile Eiyaa-Mahtuhaa while exploring the caves in the planet's tablelands. In order to study the intriguing new species, the juveniles were taken and brought back to their research bases where "horrible experiments" were performed on them. Some were placed into vats and suspended in an orange fluid. It was then that the adult members of the pack began hunting the researchers and their security forces. Over twelve people were killed in a single night.
The Eiyaa-Mahtuhaa used their abilities to mimic sound and light in order to lure the humans away. When the researchers began to catch on, the creatures changed tactics. They began destroying all of their satellite uplinks, comm stations, and even their power cores. Eventually the researchers were forced to abandon their bases, but they did devise a way to deter the Eiyaa-Mahtuhaa—ultrasonic frequencies above 180,000 Hz.
Anatomy, physiology, and behavior
Vaguely reptilian in appearance, adult Eiyaa-Mahtuhaa are 5 meters long, and have a gray dome-shaped skull blending back into a fan of six horns. Eiyaa-Mahtuhaa's eyes are located beneath the thick frontal ridge of their skull, which was set above a small, curved, bony arch, which protects an inset nose. Directly beneath their nose is a mouth that features sharp, angled teeth in the front and rows of fangs along its jaws. Two short horns grow from each side of their upper jaw, and their chin juts out into a sharp horn. Eiyaa-Mahtuhaa have long, draping muscled limbs with curving talons, which help them to climb among the gnarled trees of Erebus VII's forests. While sometimes seen walking on all four limbs, the Eiyaa-Mahtuhaa can also adopt a bipedal position.
Eiyaa-Mahtuhaa hunt in packs, being able to revise and modify their hunting plan almost instantly. While hunting, they attract their prey into a trap by mimicking sounds perfectly; they are even being able to mimic human voices. The sounds they imitate seemingly do not come from their mouths, but are projected by their inset noses. The Eiyaa-Mahtuhaa can also mimic light to attract prey. The creatures are smart enough to know when their tactics do not work, and they can change them in response. When Rion Forge was captured by an Eiyaa-Mahtuhaa pack, they also removed any equipment that she carried. After the Eiyaa-Mahtuhaa trap their prey, they spit a neurotoxin into their eyes, which acts as a neuromuscular relaxant to paralyze their victim.
Despite first appearing on the Halo 4 multiplayer map Abandon in 2012, this species went unnamed until being confirmed by Kelly Gay and Jeff Easterling on March 23, 2021 that the Eiyaa-Mahtuhaa in Halo: Point of Light were indeed the same creatures as those seen in Halo 4.
List of appearances