Remnant

The Remnants were sentient creatures encountered by the Thirteenth Doctor on Desolation. They were the result of bioengineering by scientists kidnapped and compelled to work by the Stenza.

Biology
The Remnants resembled animated strips of cloth. They lay dormant throughout daytime but sprang to life at night, either moving slithering snake-like motions or taking flight. They were capable of holding a man down and smothering him, and also had the ability to read the memories of those in their vicinity. Being capable of speech, though with voices that sounded distorted and strange to other beings, the Remnants could attempt to distract their prey with taunts about their fears and anxieties based on the memories they had extracted. The Remnants did not register as lifeforms. (TV: The Ghost Monument)

History
The Remnants were among the creatures and weapons engineered by the group of scientists whom the Stenza kept hostage on Desolation, then set free on the planet to test their ability in war. Thus, the Remnants participated in the obliteration of nearly all life on the planet.

When Ilin made Desolation the final stop in his space race the Rally, the Remnants were one of the challenges faced by the contestants — their night-time activity and innocuous appearance leading the Thirteenth Doctor to believe that the point of the Remnants in the race was to pick out the wounded at night. During the last installment of the Rally, a Remnant nearly strangled a wounded Epzo, but was injured with a knife and fled.

Later, a swarm of Remnants attacked the Doctor, her companions, Angstrom and Epzo in the Acetylene Field, with one of them latching on to the Doctor, extracting her memories of "the Timeless Child" and taunting her about it. However, the Remnants' prey managed to get the upper hand, using a cigar and the Acetylene to cause an explosion that burnt the Remnants to ashes. (TV: The Ghost Monument)

After receiving a message from the Master mentioning the "Timeless Child," the Doctor briefly flashed back on the Remnants mentioning it. (TV: Spyfall)