Spae Wife
The Spae Wife was a being that fed on the emotions of others. She was a Corri, a parasitic species that had no emotions of their own and fed on those of other beings. The Spae Wife landed in 19th century Ireland, where she was discovered by Roisin and the other members of her carnival. Roisin, who couldn't bear to see another being hurt, attempted to nurse the Spae Wife back to health because she believed she was injured. The creature latched itself onto her and possessed her, using the carnival to attract victims whose emotions she could feed on.
One member of the carnival, a Scottish man, named the creature that possessed Roisin the "Spae Wife". According to Brianna, Roisin's wife, the man said the name had something to do with witches from the Islands.
When Nyssa and the Fifth Doctor came to see the carnival, the Spae Wife took control of Nyssa's mind and attempted to force the Doctor to grant her access to his TARDIS. Tegan helped to free Nyssa from her influence, reminding her friend who she really was. (AUDIO: Feast of Fear)