Qurunx (The Power of the Doctor)

A Qurunx was being transported as cargo by a bullet train of the Toraji Transport Network in space, who appeared as a young humanoid child due to its consciousness shield making it appear as something that was to be protected.

After the train was hijacked by the CyberMasters on the orders of the Spy Master, the Qurunx was taken and tethered to a metal cyber-conversion planet surrounding Earth in 1916, hidden by a rudimentary cloaking shield until the Thirteenth Doctor disabled it, revealing the true Qurunx form.

Once freed, it was ordered by the Doctor to "disintegrate everything" with a beam, though it's destruction of the planet was temporarily diverted by the Master so that the Doctor took a fatal injury from the beam, leading to her regeneration. The Qurunx then went off into space after it successfully destroyed the planet. (TV: The Power of the Doctor)

Behind the scenes

 * In its humanoid disguise, the Qurunx was portrayed by Neo-Rae Gardener. He was uncredited.