Krafayis

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

Biology
The Krafayis are a race of bird-like reptilian creatures with an unknown origin. Their life is similar to one of a birds or vultures. They are raised and then voyage forever attacking and defending its fellow race, as well as the local races on the planets they land on. It is invisible to the naked eye but could be seen by Vincent van Gogh for unknown reasons, though it is suggested it is linked to his depression. The Doctor used a device that can identify species when it is seen in a mirror, but whether the species is only visible through reflections or the device is actually designed to see these kinds of aliens is unknown.(DW: Vincent and the Doctor)

Life Cycle
During their early life they are nurtured in a similar way as a bird would be. After several hundred years, they embark on a never ending voyage with up to three thousand other Krafayis journeying across the universe and devouring creatures they 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 Eleventh Doctor spotted the image of an unknown creature in the painting of the Church at Auvers he said that "I know evil when i see it and that is evil". When the Doctor and Amy Pond travelled back in time to 1889 after killing a young Girl the Krafayis 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 special mirror. 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 chirch the Krafayis started wondering 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 easle. Fatally wounded, the Krafayis lay there, the Doctor interpreting that it was afraid and tried to sooth 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)