Family of Blood

The Family of Blood was an incorporeal, green group mind. Because of their lack of form, they required a physical body to inhabit. They only had short lifespans. (DW: Human Nature)

Technology
They were one with their spaceship, which had the ability to turn invisible, protected by a green shield. They could also animate different things for servants (in the case of their 1913 invasion of Earth, scarecrows), although whether this was another feature of their group mind is unknown. (DW: Human Nature)

History
At somepoint in their their history they encountered the Doctor and Martha Jones and chased them throughout time and space with a stolen Time Agent vortex manipulator for the Time Lord's near-immortality, as they only had short lifespans. The Doctor was forced to turn himself Human using the Chameleon Arch to escape them, and was disguised as a teacher at a boy's school in England in 1913. (DW: Human Nature)

Ultimately, the Family's plans for immortality would end when the reconstituted Doctor destroyed their ship and imprisoned each member of the Family for all of time. The Father would be chained and left trapped on the surface of a dwarf star. The Mother was abandoned within a collapsing galaxy. The Daughter would be trapped within every mirror and it was known that the Doctor would visit her at least once a year. The Son would be trapped within the body of a scarecrow placed to watch over the field as its protector as penance for his crime.

It was also learnt why the Doctor decided to flee rather then fight the Family of Blood as it was an act of mercy. However, after the Family's ruthless attack on the village where the Doctor was present, that mercy had run out. (DW: The Family of Blood)