Race X

Race X is the mysterious alien race that appears only in the Opposing Force expansion pack and as such very little is known about them. Race X appear in the Black Mesa Research Facility only a few hours before Gordon Freeman teleported to Xen and serve as one of the main antagonists in Opposing Force.

Known entities
Race X employed several alien units during their assault on Black Mesa. Interestingly, the Race X aliens show hostility even to Xen soldiers, 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 had] never seen this species before!".

Gene Worm


The final boss of Opposing Force and one of the most mysterious of the Race X aliens, the Gene Worm attacks with streams of biotoxins and it's massive tentacles. The Creature is virtually indestructible except for it's eyes and a opening in it's belly used to summon Shock Troopers.

Pit Drone


Pit Drones generally stay in groups of five or six, and are capable of intelligent combat maneuvers. They are armed only with their scythe-like claws and rows of spines that can be fired off with sufficient force to cause injury to enemies.

Pit Worm


The Pit Worm was a massive caterpillar-like creature with an impenetrable hide and the ability to produce a searing energy beam from it's large, single eye or strike out at enemies with powerful claws. It is unknown what role (if any) these creatures serve in Race X as only one is encountered.

Shock Trooper


The Shock Trooper is the most intelligent and dangerous of the Race X aliens. Physically, they are humanoid with four arms and have a hunched posture like that of a Vortigaunt. Shock Troopers are armed with Shock Roaches and the ability to regurgitate spore grenades for use against concealed enemies. If encountered up close, they will also slash at their enemy with their claws.

Sprite


Appearing to be a flying ball of light, Sprites float throughout the Black Mesa Research Facility and all eventually led to the portal with the Gene Worm. They do not attack the player and seem to serve as a power source for Race X teleporters.

Voltigore


Large, lumbering creatures, Voltigore are gifted with the ability to create and discharge a purplish energy stream and possess thick carapaces for excellent protection, thus they serve as heavy support infantry for Race X. When critically damaged, a Voltigore explodes.

Trivia

 * No official explanation is given for the appearance of Race X on Earth in Opposing Force, though the strategy guide for the game states that the race's intentions are to invade the planet to acquire its natural resources.


 * 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 was seen in the chapter "We Are Not Alone" (floating below a crystal-topped Xen platform and emitting Sprites) and later in Worlds Collide behind the Gene Worm. 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.