Krillitane
The Krillitane were a race of creatures that could take physical features from the races they conquered. They would pick the best bits from these races.
Biology
Unable to shape-shift, they could create illusions that would keep them cloaked in human form. Since they could take the abilities from other species, their appearance and qualities could change. When the Doctor encountered them, they looked like humans with very long necks.
When not in their human-like form, they resembled large humanoid bats with skin ranging from pinkish to charcoal grey, sharp claws, and a flattened, fanged face. They slept upside down and had very sensitive hearing.
Appearances
Tardisode 3 (Webcast)
School Reunion (TV)
The Krillitane Storm (Prose)
Code of the Krillitanes (Prose)