Combine Advisor

The Combine Advisors, also known as "Shu'ulathoi" by the Vortigaunts, are the masterminds behind the Combine occupation of Earth and are commonly speculated as being the master race of the entire Combine empire.

The Advisors are large, pale, super intelligent grub-like creatures with no discernible facial features. They have a device similar to a gas mask attached to their front end, as well as a cybernetic eyepiece on the left-hand side of the faceplate.

Overview
Each Advisor wears a skin-tight olive-green body suit that covers all but the ends of their bodies, with a collar adorned with golden glyphs around their "necks." They also have a pair of thin black robotic arms implanted to their backs, capable of grabbing and lifting an adult human as well as moving the weight of the Advisor. They also have an appendage similar to a tongue in appearance, which is used similarly to a proboscis and is plunged into a weak point, such as the human neck as shown from a scene in Half-Life 2: Episode Two.

Combine Advisors have a wide range of odd vocalizations, from robotic growls and groans to loud shouting noises and screeching. Besides their technological prowess, they also appear to possess incredible psychic and telekinetic powers. They are able to communicate with others telepathically as well.

Advisor Rule
Under normal circumstances, the Advisors seem content to live in artificial seclusion. During the Combine control of Earth, a number of them lived within the Citadel and ruled the planet through Dr. Breen. They subsisted in pods during this time, reliant on life support systems.

None of the citizens of City 17 or even the Resistance seemed to be aware of their existence; the outward face of the Combine on Earth was Dr. Breen and his transhumanminions, and the Advisors seemed happy to retain this façade. However, the Vortigaunts seem to know them well and even fear them.

During the events of Half-Life 2, it becomes obvious through the increasingly agitated Breencasts that the Advisors have grown to suspect both Dr. Breen's motives and his usefulness to them, as one is shown communicating with Breen while he pleads and bargains for rescue.

With the apparent death of Wallace Breen, the Advisors seem to have taken control of the Combine on Earth directly. In Episode One, they are shown preparing to evacuate themselves from the damaged Citadel, while their soldiers and other minions are ordered to remain behind to destroy the Citadel's dark fusion reactor and send an unknown message to the Combine Overworld.

Following their escape of the Citadel, the Advisors seem to have gradually abandoned their life support systems; they have, in the words of the Vortigaunts, begun to "hatch," indicating a level of adaptation to the environment. By the time Gordon Freeman and Alyx Vance manage to shut down the life support systems of the "Barn Advisor" in Episode Two, they succeed only in making it mad.

During the events of both Episodes, they are shown to have a keen interest in Gordon and Alyx, frequently appearing on screens and in the open, monitoring their progress and dispatching Combine Soldiers to apprehend them, probably due to the fact that the duo is carrying the data packet containing Judith Mossman's transmission from the Borealis and, more importantly, the contact code for the Combine Overworld.

Abilities
Advisors possess considerable telepathic and telekinetic abilities. They are able to communicate telepathically with Dr. Breen, as demonstrated near the end of Half-Life 2, as well as the beginning chapter A Red Letter Day when Gordon accidentally teleports into Breen's office. They can also launch psychic attacks to ward off unwanted attention. Such attacks take the form of visions which obstruct the senses of those affected as well as severe headaches.

Despite their grotesque, grub-like appearances they seem to be extremely intelligent and more than capable of directly leading the Combine occupation forces on Earth in battle, appearing alongside Overwatch units in the open and orchestrating the assault on White Forest. It is unknown if they possess any understandable vocal communication abilities, though they can speak with others telepathically as demonstrated with Breen.

The telekinetic abilities of an Advisor allow it to manipulate objects in close range with considerable force. They can completely immobilize several adult humans. They are also able to levitate themselves and achieve flight, presumably with telekinesis. Though they are able to concentrate on multiple, independent objects, they cannot maintain their abilities under immense pain or physical damage. This might imply that their neurological abilities require some level of concentration or uninterrupted focus.

Though their psychic and mental abilities are exceptionally devastating, they appear to be quite vulnerable physically, at least in their "larval" forms. Besides two mechanical arms and their tongue-like appendage, they have no means of physically interacting with their environment nor any hazards they encounter; their suits do not appear to provide any armor, and their bodies as a whole are fleshy, "squishy", and bulky. One Advisor is driven off by Dog with relative ease in physical combat, and another is seen being swiftly injured by conventional weaponry. As such they seem to observe rather than directly intervene in most of their appearances.

Their "tongue" can be used to kill and extract from other beings by driving it through the neck, demonstrated on Eli and a Rebel in Episode Two. What exactly they do this for is unknown, but the events in Episode Two imply they extract nutrients or perhaps information from the brain or any nervous tissue.

Behind the scenes
their mechanical arms. There seems to be a small amount of this at the end of Episode Two when they confront Eli Vance. In the Half-Life 2 Episode 2 Game Files exist the texture of the Larval stage of the advisor unused.
 * When viewing earlier versions of the Advisor in a model viewer they appear to have another attack which utilizes
 * In Half-Life 2: Raising the Bar, Ted Backman mentions that the immense, worm-like form of the Combine Advisor was inspired by the work of Frank Herbert, most likely the images of the Spacing Guild Navigators from the Dune novels and the original 1984 film.
 * The Advisor might be partially based on the Kingpin concept, due to the similarities to the Kingpin's second design and the concept of psionic attacks.
 * The shaft seen in the Citadel in Episode One where the Advisor leaves is one of the oldest concepts created for Half-Life 2. An early WC mappack map (" ", last edited on October 12, 2001) features a prototype version of it.
 * Several different texture colors can be found in the playable Half-Life 2 Beta files. They include yellowing tones, red, blue or green. It is likely that the Advisors were to come in only one color and that these files are only experimentation.
 * In the first map of Riding Shotgun chapter, one of the screens shows an Advisor inside a wooden house. It is possible that it is the same Advisor that can be seen in Episode Two trailer due to similarities in the interior of the wooden house to the place in the trailer.
 * In the final map in Half-Life 2: Episode Two, if the player uses noclip, they can fly behind the hangar. There are two idle Advisors here. They can be damaged with weapons, causing them to actually play a sound and an animation. (If they are killed, the end cutscene will be broken.) This shows that Valve has already scripted the Advisor, possibly to be used in a future Half-Life game. Another hint is the console command sk_advisor_health 1000. Besides, a commentary from the first Advisor encounter in Episode Two suggests that the player would have to directly fight at least one Advisor in a possible Episode Three.
 * During the beginning of a scene in Half-Life 2: Episode One, the Advisor can be heard "speaking" while it is on a screen, just before Combine soldiers come out. This is actually the sound of Vortigaunts from the original Half-Lifeslowed down. If this is indeed the Advisor speaking this suggests that they speak the same language as the Vortigaunts, although this is most likely just recycling old sounds.
 * An unused particle system "advisor_psychic_shield", found within the Episode Two game files, suggests that Advisors were to be seen using some kind of an energy shield.
 * Spawning the Advisor in Half-Life 2: Episode Two crashes the game, most likely because the Advisor only appears when scripted.
 * While it may seem that the Advisors do not possess any actual AI, this is in fact false. In the Source SDK, npc_advisor_shared.h includes this line: #define NPC_ADVISOR_HAS_BEHAVIOR 0.. If set to 1 and compiled, the Advisor will pick up objects with its telekinesis and throw them at the player, as well as forming a makeshift shield with any physics objects at hand.
 * The Half-Life 2 model also has some unused animations.