Race X

The Race X is a mysterious alien race appearing in the Black Mesa Research Facility a few hours before Gordon Freeman teleports to Xen, serving as one of the main antagonists in Opposing Force.

Overview
Race X consists of several alien creatures, ranging from average to large. They also use their own weapons, such as the Shock Roach and the Spore Launcher, as well as natural defenses, such as toxic spits or claws.

Race X did not seem particularly well adapted to the borderworld Xen, from which no creature is native, hence their lack of presence on Xen in Opposing Force. Their original homeworld lays "somewhere beyond".

The Race X aliens show hostility even to Xen units, suggesting that they are not allied and belong to different factions from different worlds/dimensions. This is further suggested when a scientist abducted by a Shock Trooper calls out that he has "never seen this species before".

Some of them are studied in Black Mesa's Sector E Biodome Complex.

Known entities

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

Behind the scenes
Created by Gearbox, the Race X only appears in Opposing Force; therefore very little is known about them, as they do not appear nor are mentioned in any other game of the series. No explanation is ever given for their appearance on Earth, although the Opposing Force strategy guide states that the race's intentions are to invade the planet to acquire its natural resources. Regardless, the general consensus is that they probably will never be seen again in the series.

Some explanation and clarifications about the Race X and their place in the Half-Life universe is given by series' writer Marc Laidlaw on the Marc Laidlaw Vault on the HalfLife2.net Forums. There he states that Race X is purely a Gearbox creation that does not figure at all in his thinking about the Half-Life universe (although his level of input into its creation, if any, is unknown). He furthers adds that the Gearbox team wanted to come up with a set of creatures that would create gameplay they knew how to make, and that they could have been making an original title or an add-on for any other franchise, and plugged Race X into it - the reason being that they had gameplay they wanted to explore and needed the freedom of their own race of critters to conduct those experiments with. He also suggests that if Gearbox had kept making games set in the Half-Life universe, more about the Race X would have been revealed.

Trivia

 * While both Race X and Xen aliens use teleport technology, their portals have different colors: Xen portals appear green, whereas Race X portals are purple. The latter can be seen in the chapter We Are Not Alone (floating below a crystal-topped Xen platform which appears to be powering it and emitting Sprites) and later in the chapter Worlds Collide, behind the Gene Worm, and even inside the Gene Worm's chest cavity. It seems that in order for Race X to ever reach Earth at all, they must detour through the border world and use the crystals there to charge their portals.
 * The Tentacle creatures featured in original Half-Life are speculated to be members of Race X, due to their similarity to Gene Worm. Other theories suggest that they are, in fact, body parts (tentacles) of the Gene Worm itself.

List of appearances

 * Half-Life: Opposing Force