Timeless Child's species

The Timeless Child's species were a largely unknown species from another universe or dimension, being, according to, the Doctor's original species as the Timeless Child.

Biology
They resembled Time Lords externally, and were able to regenerate. It was unclear how many times they could regenerate, and it may have been infinitely; Tecteun limited the number to twelve upon the creation of the Time Lord race. (TV: The Timeless Children)

Life cycle
When a member of this species was severely injured, their bodies would emit regeneration energy that could cause damage to the surrounding area. When this happened, their appearance would change as well as their personality. (TV: The Timeless Children)

History
The Timeless Child, the only known member of this species, was found near a boundary to another reality or dimension, from which they had come through, seemingly having been dumped on a random planet near a monument.

After being brought to Gallifrey by the Shobogan Tecteun, the Timeless Child's biodata was used as a template to allow for regeneration in other Shobogans within the Citadel. Copying this ability had allowed them to become Time Lords, with noting that a little bit of the Doctor had been inside him all along. However, their copied version was limited to sets of twelve, though this appeared to be a decision made by Tecteun rather than a shortcoming. (TV: The Timeless Children)