Race X

Race X is a hostile alien race that appear only in the Opposing Force expansion pack, and very little is revealed about them. Race X aliens appear late in the timeline of Half-Life, only a few hours before Gordon Freeman has teleported to Xen (an event that takes place in both Half-Life and Opposing Force). No explanation is given for the appearance of Race X aliens on Earth in-game, though the official strategy guide states that the race's intentions are to invade the planet to acquire its natural resources.

Military

 * Pit Drone
 * Shock Trooper
 * Voltigore
 * Pit Worm
 * Gene Worm
 * Sprite