Empathivore

Empathivores were creatures that fed on emotion.

Biology
The Empathivore encountered on Grått was a large, hairy, black creature with four eyes and many limbs.

An empathivore fed off emotions, including happiness, sadness and fear. An empathivore could sense the strength of emotions and who was creating them. If an empathivore consumed too much emotion, it exploded and died. It grew as it absorbed more emotion. The Grått specimen grew from slightly larger than a man to a giant that could easily pick up the TARDIS.

History
An empathivore arrived on Grått at some point and killed several locals. Known as the Mörkön, the monster became less dangerous after the Gråttites abandoned emotion. A Gråttite known as Grayla reintroduced emotions to Grått and reawakened the Mörkön. The Tenth Doctor and Martha Jones later visited the planet and defeated the Mörkön by overflowing it with emotion.