Flux imp

 was a prisoner of the two Varaxils who crash-landed on Vetter's Tor in the 1650s.

Its home was 480 light-years away from Earth in the Pherkad Array. It had horns and hooves.

It was captured by the "Lucern" and "Finicia" because it was an Odic channeller. It was kept in a Lokic containment web.

It was slowly dying because of a discharge from a fractured power cell. The Eighth Doctor was too late to save it but stayed with it till the end.

Beatrix Butcher thought it was the Devil and accused the Doctor of consorting with him, causing both the Doctor and herself being imprisoned by John Kincaid, the Witch-Pricker. (AUDIO: The Witch from the Well)