Hailing from the best turn based strategy game ever, X-Com: UFO Defense, the creatures of X-Com are varied and seem based on a variety of popular modern myths regarding the appearence of extraterristrials while also invoking the ideas of genetic engineering, cross breeding and other beliefs encountered in the whole alien abduction phenomenon. Below is a complete bestiary for all of the alien creatures found in X-Com: UFO Defense. This information is courtesy of the X-Com ufopedia.

Sectoid, The Sectoid Hierarchy ranges from soldiers to leaders with powerful psionic abilities. These psionic powers can be used to demoralise soldiers in combat, or even take control of their minds. They tend to indulge in human abductions and cattle mutilation. The abduction is used to extract genetic material for cross breeding and developing clones for infiltrating human society. The cattle provide both nutrition and genetic material. This race appears to want to develop superior genetic hybrids to increase the efficiency of their hive-like society.

Cyberdisc This miniature flying saucer is an automated terror weapon armed with a powerful plasma beam. The anti-grav propulsion gives it a big advantage in difficult terrain. Its primary function is destruction and terror in the service of the Sectoid race.

Floaters The Floaters are primarily soldiers and terror agents. They are naturally predatory beasts, genetically engineered and cybernetically enhanced to make formidable warriors. The lower half of the body and most internal organs are surgically removed, and a life support system is installed. This implant contains an anti-grav unit which enables the creature to float, albeit unsteadily, through the air.

Reaper This bipedal carnivore has powerful jaws and a voracious appetite. It has a number of brain implants which are used to control its activity. The primitive predatory instincts of this creature are of little use except to terrorise and destroy. Reapers are commonly associated with Floaters.

Snake Men This race developed in an extremely hostile environment. They are extremely tough and can resist extreme temperature variations. Their mobility depends on a snake-like giant 'foot' which protects all the vital organs. Their objectives appear to be purely predatory and they appear to be under the command of some other Intelligence which directs their military-style incursions on earth.

Chryssalids The crab like claws of this creature are a powerful weapon in close combat. The high metabolism and strength of this creature give it speed and dexterity. Instead of killing its victim it impregnates it with an egg and injects a venom which turns it into a walking zombie. A new Chryssalid will burst from the victim shortly after impregnation. Chryssalids are associated with the Snakeman race.

Mutons This humanoid creature is physically powerful and intelligent. They have a particular appetite for consuming raw flesh of any kind, which they need for sustenance like earth based carnivores. They appear to rely on telepathic commands from a race known as 'Ethereals'. Once separated from this telepathic link their mental system appears to break down and they die. The cybernetic implants are used to enhance their combat performance. They are clearly the foot soldiers for a higher intelligence.

Etherals This being has awesome mental powers which allow for telepathic communication and telekinetic abilities. The apparently weak physical abilities of this creature are sustained by its mental powers. We do not understand how these telekinetic powers work, since they seem to defy the laws of physics as we know them. They are extremely dangerous in any combat situation, where they rely on their mental powers for combat. They rarely appear on earth since they seem to rely on other races to pursue their objectives.

Sectopod Sectopods are robot creatures with a powerful plasma beam weapon. The control if these mechanical beasts is via a telepathic link to their controllers, the Ethereals. Sectopods are the most powerful terror weapon available to the alien forces.

Celitid This life-form has the mysterious natural ability to float through the air. It appears to detect human brain waves and will move towards a human target even if well hidden. Once a target is detected the Celatid lands and fires small globules of extremely corrosive venom. The creature has the ability to clone itself at an alarming rate. It accompanies the Muton race in its wonderings.

Silacoid This silicon based life form generates an enormous amount of heat. It has the strength to crush rocks which can then be ingested by the hot core. It has a primitive intelligence and can be controlled by implants or telepathic beings. It works with the Muton alien race.