The Nihilanth attacks by launching energy balls, which come in two types: a swarm of purple-colored electrical orbs that causes immense damage, and a slow-moving, green-colored orb (similar in appearance to the teleportation portals constructed in the Black Mesa Research Facility) which homes in on and teleports its target to other sections of its lair populated by Xen aliens. Its unusually long arms end in disproportionately huge hands and fingers, and it wears metallic wristbands, which look similar to bands worn by the Vortigaunts. Like the rest of the intelligent Xen races, the Nihilanth has a third appendage protruding from the middle of its pectoral chest region. The creature sits on a large mechanical levitating contraption consisting of a large base with spikes underneath. Its legs, minuscule in relation to its body, appear either to be vestigial, or are the remains of amputation. Physically, the Nihilanth resembles a gigantic, oddly-proportioned fetus with its head alone outsizing the rest of the body, and its brain cavity forming most of the head's bulk.
