Vigil

The Vigil were responsible for the sacrifice of the Queen of Years, should she choose not to sacrifice herself.

Three Vigil attempted to fulfil their duties when the Doctor and Clara protected the Queen of Years, but disappeared after they had failed, as the Old God had no further need of them.

Abilities
The Vigil had very soft voices and were terrifying to most people who encountered them. In battle they had powerful telekinetic powers which could be used to hurl their victims or shield themselves from attack. However even when all three of them were attacking at once, they were unable to overcome the Doctor who defended himself with his Sonic Screwdriver, indicating that their abilities were sound-based in some fashion.

The Vigil also possessed the ability to teleport, appearing from a black hole in order to get from place to place. (TV: ''The Rings of Akhaten)