Axos

Axos came to Earth to supposedly in need of fuel, but its real motivations were to drain all energy from Earth.

Axonite
Axonite was the miracle element that the Axons traded with Mr Chinn for the energy to re-fuel their ship, it was sent remarkably fast around the world to key scientific points, where it would drain energy evenly from those points.

Axons
The Axons had humanoid features, they were part of the main Axos structure. They were capable of morphing between various humanoid shapes and teleporting themselves and others.

History
Axos encountered the Master at an unknown point in time, at that time they captured his TARDIS, he in turn directed them toward Earth. Following their arrival on Earth and attempt to start a 'feeding cycle' the Doctor placed their ship and all of Axos in a time loop.