Krafayis

The Krafayis were a species of space-faring omnivirous predators.

Biology
The Krafayis are a race of bird-like reptilian creatures. Their planet of origin is unknown. They travel through the universe, feeding on the people and animals on the planets they land on. They are invisible to the naked eye, but one could be seen by Vincent van Gogh for unknown reasons, perhaps due to Van Gogh's unique way of perceiving the world around him or it could be linked to his depression. The Doctor used a device with a mirror that could identify and show the creature's image, but whether the species is only visible through reflections or if the device is actually designed to see these kinds of creatures is unknown. (DW: Vincent and the Doctor)

Life cycle
Large groups of Krafayis, numbering up to thousands at a time, would journey across the universe, landing on planets and devouring any creatures they would find. They are ruthless, and will not return for those Krafayis left behind on a planet they have hunted on, leaving them to fend for themselves. It is hinted that they leave the weak behind, such as the Krafayis left on Earth due to its blindness. (DW: Vincent and the Doctor)

History
The Krafayis have travelled the universe since the late Dark Times and have a unique defence system where they cannot be seen by the naked eye. They have voyaged across the universe in packs and devouring many life forms. One was left behind on Earth and was scavanging on humans. This Krafayis could only be seen by the Famous Artist Vincent van Gogh. When the Doctor and Amy Pond travelled back in time to 1889 after seeing the Krafayis painted in van Gogh's Church at Auvers, they discovered the body of a young Girl the Krafayis had attacked. The Krafayis later attacked Amy, prompting Vincent and the Doctor to come to her aid. The Doctor could not see it, but later saw and identified the Krafayis with a Visual Recognition Device. Later on, when Vincent started painting the Church at Auvers he spotted the Krafayis through one of the church windows, as seen in his painting in 2010. When the Doctor attempted to confront the Krafayis the creature attacked. When the Doctor, Amy and Vincent attempted to hide in the church the Krafayis started wandering around the room as if it were lost. The Doctor realised that it was blind and that was the reason it had been left on Earth. However before the Doctor could make peace with the Krafayis, the creature charged towards them, inadvertently impaling itself on van Gogh's easel. Fatally wounded, the Krafayis lay there, the Doctor interpreting that it was afraid and trying to soothe it. Vincent genuinely felt remorse for the creature's death, feeling that he shared some similarities to it due to their treatment by their peers. He noted that "It wasn't without mercy at all, but without sight". (DW: Vincent and the Doctor)