Qurunx

The Qurunx (pronunciation: kwʌrəŋks/kwu-runks) were creatures of sentient energy, described by the Thirteenth Doctor as "one of the great mysteries of the universe", "rare", and had "enough [energy] to power planets and civilisations". They resembled large ethereal jellyfish, with long thin tendrils glowing with blue and orange light. They utilised consciousness shields as a defence, being able to disguise themselves to the observer as something that they would instinctively want to protect, such as a child. The energy that they produced could also be channelled into a beam capable of disintegrating planets.

One Qurunx, being transported by a bullet train of the Toraji Transport Network in space, had been taken by the CyberMasters and tethered to a metal cyber-conversion planet surrounding Earth, powering it in the process. It was hidden with a rudimentary cloaking shield. Once freed by the Thirteenth Doctor, it was ordered by to "disintegrate everything", though it was temporarily diverted into mortally wounding her instead by the Spy Master, leading to her regeneration. (TV: The Power of the Doctor)