Gargantua

The Gargantua are large biomechanical beasts which participated in the Nihilanth's invasion of Black Mesa.

Overview
During the resonance cascade of Black Mesa, the Gargantua were one of alien species teleported from Xen to Earth, where they represented the heavy armour of the Nihilanth's army. An average Gargantua stands at 20ft tall and is coated entirely in blue and grey armour, seemingly a metallic skin rather than a simple armour suit, capable of withstanding immense damage and vulnerable only to explosives, energy weapons and significant electrical discharge. They each have a single red eye and their arms end in mollusc-like pincers capable of projected immense heat, incinerating anything within range of this attack. Like the other sapient species of Xen (the Vortigaunts, the Grunts, the Controllers and the Nihilanth itself), Gargantua feature two vestigial limbs present in the middle of the torso, although they are placed noticeably lower than that of its counterparts, who also have only one of these limbs as opposed to two.

At least three Gargantua were present in Black Mesa during the resonance cascade, all of which were killed. Two more were encountered by Dr. Gordon Freeman on Xen. Since the death of the Nihilanth, the status of the Gargantua is unknown.