Timeless Child's species

According to one account, the Doctor's original species, as the Timeless Child, held the ability to regenerate into new bodies indefinitely. The Timeless Child, the only known member of this species, was found near a boundary to another reality or dimension.

After being brought to 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. In this version of events, this was the origin of the Time Lords; noted that a little bit of the Doctor had been inside him all along. (TV: The Timeless Children)

Life cycle
When this species gets severely injured, their bodies will emit a huge amount of golden energy that may cause huge amounts of damage to the surrounding area.

When this happens, their appearances will change as well as their personalities. They can do this regenerative ability an infinite amount of times.