There is a life form in this Universe, an alien life form, no too dissimilar to a virus. This life form is minute and deadly, it floats aimlessly throughout the Universe, and if ever one tiny molecule of this lethal alien virus hit our planet, the consequences would be extreme and ultimately terminal.
The alien virus has a name, its name is Irazion, the Irazion travel alone seeking worlds to devour, the Irazion are intelligent in their own special way. The Irazion are loners, they do not like the company of other Irazion’s, or for that matter anything unless it is devouring it.
Unbeknown to some of the Irazion population, because of their small size, some are held captive by incredibly intelligent species, called, Kllar. The Kllar infiltrate developing worlds and over a period of time determine whether they are suitable to survive, to continue on to make an intergalactic developed species, or to be destroyed. They give each world a chance, a good chance to show that they are capable of showing civilisation. If after a period of time the world does not live up to expectations the Kllar, they release one molecule of the Irazion into the unfortunate, unsuspecting world.
The Irazion quickly multiplies after initial release; before long the world in question sees a slow decline in sea creatures then land animals start to die. The death is slow and extremely painful, once the Irazion enters the body of a host it infects the blood stream, and slowly kills the far extremities. If one ever entered a human being it would attack the feet, fingers, ears, nose, and genitalia, of its host.
Agonising pain is so extreme that each infected part has to be amputated, apart from the ears, nose and genitals, which die and after massive trauma and pain, fall off. Each body part in turn is infected then the pain increases until it is so severe, amputation is the only short term release. Eventually the Irazion reaches the main organs and the host mercifully dies.
Everything on the planet is then gradually infected by the Irazion, some lucky living creatures die instantly when the Irazion enters its body, the unlucky ones survive and linger. They are left mutated, because of amputation, severe illness and are very weak. They cannot look after themselves and no-one is left alive who is capable of looking after them, they die a slow agonising death.
Eventually, the Irazion exhausts the planets life force and becomes dormant. The Kllar then obliterate the planet out of existence.