Furies

The Furies were creatures that lived in the Time Vortex.

Outside the vortex, they looked like snakes with jackal-like heads. They hunted by mindscent, and petrified their victims. Their victims and Time Lords were the only ones who could remember them, and could not even be recorded on electronic devices.

Whilst in the vortex they could outrun a TARDIS, but in the normal universe they were considerably slower. They could mistake innocent bystanders for their intended prey. Easily upset, it was extremely hard to banish or kill them. Once they had their prey's mindscent, it was not possible to escape them.

The Curia of Nineteen used Furies to eliminate threats to their Realm. (PROSE: The Suns of Caresh)