XVI is a virus-like organism that lives in the blood and bone marrow of infected creatures. The organism is psionically powerful, and links together with other organisms to create a distributed intelligence, like a network of tiny computers hooking together to form a more intelligent one.
Singly, XVI hosts are quite stupid, reduced to bare instincts. It takes approximately 8-10 XVI-carrying hosts together to create a mind with human-like intelligence. However, each additional host makes the group a tiny bit more intelligent, and the alien mothership has a population numbering in the trillions. The only things limiting this alien mind are the scope and nature of its own thoughts and instincts.
XVI's most powerful internal urge is to spread and become more intelligent. Its goals, therefore, are to create a version of itself capable of infecting and thereby enslaving the human race. Initially none of the various XVI strains can penetrate the human immune system, but after enough research and acquiring of tissue samples, a new XVI strain is engineered to infect humans.
The infection spreads by the direct injection of infected blood into a new host. The organism fools the victim's immune system long enough to settle in the victim's bone marrow, where it starts to change all newly-created defensive cells to ignore XVI and destroy the old defensive cells.
This results in a feeling of extreme illness for the victim, lasting anywhere between 30 seconds and 30 minutes, depending on the severity of infection. This period is marked by severe vomiting, erratic behaviour, and discolouration of the skin in the form of red and grey blotches. Eventually the skin will turn entirely pink-grey as XVI eliminates the remnants of the old immune system.
Once XVI has a good hold on the victim, it will psionically control the victim's every move, and he or she will be hostile to any PHALANX operatives.
Alien bases will be the centres of XVI spread on Earth. Knocking out an alien base will allow the area around it to recover, especially if the player researches XVI counter-virii, but many of the infected will simply flee to other areas.
Incorporation & TODO
The idea is for the player to wage a biological war against XVI for control of Earth. XVI spreads, PHALANX attempts to create new vaccines, XVI counters the vaccines. Each successful vaccine or alien base mission will buy the player some time, but XVI cannot be defeated without destroying the alien mothership.