Flood combat form
A Flood combat form is the product of Flood Super Cells, typically via a Pod infector, infecting a sentient host organism. They serve as the Flood's primary combatants, defending the Flood against attack and securing additional hosts for infection.
When a Pod infector successfully enters a host body, it takes over the organism's nervous system and mutates its body using Flood Super Cells; inhalation of spores can have the same effect. During the infection process, the host's internal organs are broken down, and the resultant nutrient stockpile is used to develop the tentacles, claws and various other appendages and apparatuses. Combat forms can spread the Super Cell merely through wounding a victim, though such infection may progress gradually. If the combat form is infected by a Pod infector, it maintains the infector's red sensory appendages as an impromptu central nervous system until the host has been completely assimilated.
Both living and deceased hosts can be infected, although the infection process is inherently fatal to living hosts. If the host is still living when initially infected, or at the very least has not suffered somatic brain cell death, the Flood is able to retrieve comparatively vast quantities of information from the host's memory, ranging from muscle memory to specific coordinates, access codes, flight protocols, etc. Once it has total control over the host's corpse, the Pod infector changes the physiology of the body to better suit its own needs. As combat forms retain most of the host's abilities they are able to utilize their host's weapons and vehicles, albeit with less finesse.
On rare occasions, weak or damaged Pod infectors cannot properly take over a host, allowing the host to survive, even retaining some control and consciousness, as in the case of Private First Class Wallace Jenkins.
In the initial stage of a Flood outbreak, the Feral Stage, combat forms communicate using pheromones and have one instinctual behavior: to secure new hosts to strengthen the local controlling intelligence. It is to be noted that a group of Flood will occasionally go after Sentinels if they are perceived to be the greatest threat in an area, even though Sentinels are unable to be infected by the Flood due to their inorganic nature.
Once a sufficient store of biomass is available the Flood enters the Coordinated Stage, and begins forming pure form Flood, with the combat forms being used either as defensive units or calcium/biomass reserves.
Flood infection is a rapid and efficient biological process, as it can take under a minute in certain cases. Infected hosts are rapidly digested while being converted, which leaves the host severely ravaged and decayed, much like a corpse that had been exhumed a few weeks after its burial. Over time, the combat form begins to generate new Pod infectors in its back, transforming it into a carrier form once it has outlived its combat utility. In the field manual it says that an effective tactic is to shoot at the limbs or head.
Types of combat forms
Virtually any creature can be infected to become a combat form, but the most frequently-used hosts are Sangheili, humans and Jiralhanae. Unggoy and Kig-Yar can be used as combat forms, but this is uncommon due to their weaker body structure. A small number of species are known to be immune to conversion, including the Mgalekgolo/Lekgolo (which are composed of boneless worms that do not have a central nervous system), the Yanme'e, whose exoskeleton lacks the required amount of calcium which renders infection impossible, and the Huragok which is an artificial organism, and therefore believed to be immune.
All victims of the Flood's infection, regardless of their physiology, will undergo a similar mutation process. The skin decays rapidly, and changes to the color and texture of Flood biomass as the Flood Super Cells overtake the body. The host's arm bones elongate and grow into whip or claw-like appendages, which will serve as their primary melee weapon in close-combat situations. As the Pod infector now serves as the host's "brain", the head is usually forced aside, and can be severed without any effect on the combat form.[notes 1]
The human combat form is significantly smaller than other forms due to their hosts' smaller stature. As with other combat forms, it is capable of sustaining massive physical damage before being unusable to the Flood. Although it cannot take as much damage as the Sangheili combat form, the human form has some advantages, being more agile, harder to hit due to its small size, and quicker to melee an opponent. The head of the combat form is pushed to the right side of the body to make room for the Pod infector.
No actual examples of Flood-infected Spartans are known to exist. The UNSC Infinity's War Games combat training deck features simulations of Spartan-IV combat forms, which may have been based on conjecture or on information from actual encounters. Some SPARTAN-IV personnel volunteer for assignment to Flood containment Fireteams, who have routinely dealt with Flood outbreaks in the Post-Covenant War conflicts. Should a Spartan become infected by the parasite, UNSC cryptonym CORRUPTER is declared, authorising weapons of mass destruction for immediate release.
Simulated Flood-infected SPARTAN-IV personnel bear several differences from standard human combat forms. The right arm is converted into a pincer-like, bladed appendage, and the left leg sustains similarly drastic mutations. Exposed parts of the body are covered with what appear to be calcareous plates, and red "muscle" tissue can be seen in the gaps between plates. A large hump or tumor-like growth on the back is apparent, perhaps serving to shield the Pod infector. Perhaps because of the obstructing bodysuit, the typical Flood sensory tentacles do not protrude from the chest cavity. The form appears to retain more of its original silhouette than typical combat forms. Although most of the Spartan's armor is discarded, the components responsible for generating the energy shield are retained. UNSC War Games have also simulated infected SPARTAN-II personnel, featuring mostly intact armor plating except for the neck and head region, where the helmet is cracked and the remains of the victim's skull are visible. These infected SPARTAN-IIs have large Flood biomass growth around their head, with their jaws dislocated to allow the emergence of a Flood tendril.
The Sangheili combat form is agile, resilient, and capable of utilizing its host's armor abilities such as active camouflage and energy shields to assist them in combat. The Sangheili combat forms are slightly larger than the human form and as such present a larger target. The head of the combat form is typically slung over the right shoulder, the neck bones having been "liquefied" during infection.
The Jiralhanae combat form is a formidable enemy and is more aggressive in combat than other combat forms, as it will charge towards an opponent recklessly; this behavior is most likely a holdover from the Jiralhanae's savage nature and preference for close combat. The Jiralhanae form is more powerful than the human form, but falls short against the Sangheili form. It is bulkier and slower than other combat forms. Since a Jiralhanae cannot be infected until their power armor is destroyed, the Jiralhanae form cannot make use of their host's armor abilities. During infection, the Pod infector often burrows into the mouth of a Jiralhanae, pushing the lower jaw and rest of the head apart to fit into the body. The infected Jiralhanae combat form displays a scream-like expression. This is in contrast to the infecton process of humans and Sangheili, where the Pod infector typically burrows into the left side of the chest of its victim. However this isn't always the case.
Unggoy and Kig-Yar combat forms
Rarely seen in actual combat situations, infected Unggoy and Kig-Yar are more commonly converted into carrier forms or processed for their biomass.[notes 2] These "building blocks" can be used to add to a Gravemind's superstructure or be molded into Flood pure forms.
Forerunner combat forms
Halo: Combat Evolved
Halo: Combat Evolved Anniversary
Halo 2: Anniversary
List of appearances