Family of Blood
The Family of Blood were a family of hunters who attempted to take his near-immortality away from the Tenth Doctor.
Biology
They were green, gaseous predators that could inhabit and control human bodies. Before they took human form, they were kept in small, spherical receptacles. Their lifespans were short and would perish in just three months if they went without possessing anyone.
While in human form, the Family could telepathically communicate with each other from a distance.
They also had a very good sense of smell and could track people by scent alone.
Appearances
Human Nature/The Family of Blood (TV)