Rutan

The Rutan are a non humanoid, technologically advanced species from the Doctor Who universe.

Physiology
Essetialy they are large green spheres with tentacles that are a few feet in diameter.

They have the ability to take the form of any creature they desire, they can also generate lethal bioelectrical shocks. despite having no visible mouth they can speek.

They seem to absorb electrical energy for sustenance

History
They are at war with the Sontaran Empire which has been going on for fifty thousand years and never ends despite the sontaran empire only lasting another ten thousand years (this might sugest that the rutan host are winning the war, as the Sontarans would never serender, even if they were almost wiped out.).