Eknodine

The Eknodine were a species of aliens that took over the bodies of elderly humans in a dream created by the Dream Lord.

Biology
The Eknodine appeared as aliens that could live inside human hosts, extending their lifespan and increasing their physical strength. Though most of the body of the Eknodine was hidden inside the human host, a green eyestalk could be extended from the mouth, which would spray out a green cloud when attacking. This cloud could turn humans into dust. They also had thin tendrils that protruded from the eyestalks. (TV: Amy's Choice)

History
The Eknodine that the Eleventh Doctor, Amy Pond and Rory Williams encountered in a dream said that they were driven away from their home planet and came to Earth, where they took hosts at the Leadworth retirement home to stay inconspicuous. Angered at their loss, they decided to destroy other worlds.

After the Doctor, Amy and Rory found out that the Eknodine had possessed the humans, they chased the trio and cornered them in Amy and Rory's house, attempting to then gain entry. One, in the guise of Mrs. Poggit, climbed to the top floor window and killed Rory, turning him into dust. The Doctor used a lamp from the baby-to-be's bedroom to make the Eknodine fall from the roof, presumably killing it. Amy and the Doctor decided to kill themselves, hoping that this was the dream, and used a van to run a couple of Eknodine over, before crashing into the house and "dying". (TV: Amy's Choice)