Nihilanth

The Nihilanth is the final boss in Valve's first-person shooter Half-Life. In the game, the Nihilanth is the controlling intelligence behind the invasion of Earth. Hovering silently in an enclosed cavern dozens of stories tall, it has been commanding the forces of Xen and holding open a dimensional rift connecting Xen to Earth, enabling its creatures to attack.

Physical Attributes
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. Its legs, minuscule in relation to its body, appear either to be vestigial, or are the remains of amputation. The creature sits on a large mechanical levitating contraption consisting of a large base with spikes underneath. Like the rest of the intelligent Xen races, the Nihilanth has a third appendage protruding from the middle of its pectoral chest region. 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.

Attack Methods
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. It also uses these green orbs to teleport Vortigaunts and other Xen creatures into its main chamber to help defend it against intruders. This may not be intended as the creatures appear only when the green orb flies into a wall or rock or is destroyed by the player and triggers the teleportation. A series of gold-colored "energy spheres" orbit around the Nihilanth's head, rendering it impervious to damage. These are consumed as the Nihilanth suffers damage from the player, but specialized crystals within the upper portion of its chamber replenish the spheres as they vanish. When the player destroys these crystals and does sufficient damage to its body so that all the "energy spheres" are consumed, the Nihilanth's head opens up like a flower, revealing a shining, massive portal as was described by the scientist who tasked you with taking it out (they were aware that this opposing portal was created by the intense mental strength of another being). Sufficiently damaging this portal destroys the Nihilanth. Additionally, once the Nihilanth uses up all its golden energy orbs, and cannot replenish them, it can only attack with one electrical orb, instead of a swarm of ten, or a teleportation orb.