Glass avatar

The Glass people (TV: Twice Upon a Time), are translucent humanoids made out of glass.

History
Helen Clay started up the Testimony Foundation, a foundation of taking people from their last moments and making them into glass bodies, in 500000012 on New Earth (TV: Twice Upon a Time).

When one glass person tried to take Captain Lethbridge Stewert, there was a timeline error during the process, putting the Captain into the wrong decade. The glass people then took the The TARDIS, with the Captain and the two Doctors inside. While investigating the Ship, the First and Twelfth Doctors find the glass woman, who shows that they have "found" Bill Potts, as a glass person.

After finding out about Testimony, the Doctor decides to put the Captain back to the time of his death. After the Captain's and first Doctor's farewells to the Twelfth Doctor, Bill shows the Doctor herself, but as Clara Oswald, making the Doctor regain his memories of her (TV: Hell Bent). Then, another glass person as Nardole walks up to the Doctor. The Doctor gives one last hug to Bill and Nardole before they teleport away (TV: Twice Upon a Time).