Iska'lanz'rm

The  Iska'lanz'rm  were an alien race created by the imagination of a human boy named Harry Ware. The Tenth Doctor encountered them while travelling with Martha Jones.

Biology
The Iska'lanz'rm were a humanoid race. They resembled upright cows with brown fur, and white patches of fur on their head and neck. They had hooves in place of feet and sharp claws on their hands. Where their eyes should have been, yellow serpents protruded, each with a singular eye and a large gaping mouth underneath. (PROSE: The Box Under the Tree)

Hhistory
The Iska'lanz'rm were created by the universe, which had observed Harry writing the story of their war with the Xarantharax. By the 21st century, this war had begun.

In December 2008, the Iska'lanz'rm came to Earth to stop Harry from drawing a picture which would end their war and cause the two races to declare peace with each other. (PROSE: The Box Under the Tree)