Flood combat form

A Flood Combat Form is an organism suitable for combat that has been infected by the Flood parasite via an Infection Form or Flood Spores. The victim is mutated into a combat unit that fights for the Flood. They coordinate attacks on certain enemies by a Gravemind, if there is one.

Pathology
A Combat Form is not a natural organism, but rather a mutated host infected by parasitic Flood Super Cells implanted by an Infection Form. Successful creation of a Combat Form requires a host with sufficient biomass and calcium store. After mutation begins, the infection form attaches with a protruding neural connection that allows it to command the host's nervous system, thus rendering command of the legs and arms useless. During the infection process, the host's internal organs are liquefied and the nutrients from them are used to develop the tentacles and other appendages.

The host stays alive during and after the transformation process and can be conscious and aware even after the final transformation. The victim is kept alive after infection so that it lasts longer as fuel for the Infection Form. This process is presumably very painful and terrifying. Once fully transformed, the Infection Form has total control over the host's body and changes the physical appearance of the host to better suit its own needs (although an infected host will be roughly the same size as it was before). On rare occasions, this effect may be weakened by time in stasis, allowing the host to regain some control, as in the case of Private First Class Wallace Jenkins. Combat Forms retain the host's previous attributes and so can single wield weapons, and drive and board enemy vehicles. However, Infection Forms do not require their hosts to still be alive for infection. Even dead hosts are suitable for conversion into a Combat Form, reanimating again after being infected; though the brain tissue remains dead, the victim's biomass and calcium reserves are sufficient to warrant infection.

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. Once a sufficient store of biomass is available for the Flood to enter the Coordinated Stage and begin forming Pure Form Flood, the Combat Forms are used either as defensive units or calcium/biomass reserves. According to the John-117, a Sangheili Combat Form looked like a Sangheili, except it appeared that someone had "killed him, buried the body, and dug it up two weeks later". Flood infection is a rapid and efficient biological process, which can take under a minute in extreme cases. The Flood can recognize if a potential host is immune, and will focus on that organism above all other threats in the area. A group of Flood will occasionally go after Sentinels if they are perceived to be the greatest threat in the area, although Sentinels are unable to be infected by the Flood.

Types of Combat Forms
A specific creature is needed for the infection and creation of a Combat Form. Of the various Covenant races, only a few species meet the necessary requirements. Species known to be immune to conversion include the Mgalekgolo and Lekgolo, whose complete lack of skeletal calcium (i.e. bones), colonial physiology and insignificant biomass per individual worm make infection and neural synchronization impossible for Infection Forms, the Yanme'e whose exoskeleton lacks the required amount of calcium renders infection impossible, and the Huragok which is an artificial and gas-based organism and therefore believed to be immune.

All victims of the Flood's infection, regardless of their physiology, will undergo the reanimation process where the hosts will experience its skin decaying rapidly (if they were infected while alive), growing whip-like appendages which will serve as their primary melee weapon in close-combat situation and have their heads pushed aside/apart to provide space for the Infection Form to rest itself on the host' chest. In Halo 3, the reanimation process can be witnessed; the host will twitch around in pain, and eventually collapse on the ground. Afterward, the whip appendages will force itself out of host's left arm, and the Infection Form will force itself out of the host's chest.

If available, the Combat Forms are able wield the arsenals of the UNSC and those of the Covenant. In Halo 2, all Combat Forms are also capable of driving and boarding vehicles and are able to do so in Halo 3, though the ability to drive vehicles is lost.



Human Form
The Human Combat Form is significantly smaller than other forms due to their original smaller size. As with other Combat Forms, it is capable of sustaining massive physical damage before being unusable to the Flood controller; in fact, as long as the chest cavity and legs remain intact, it will continue to fight. Although it cannot take as much damage as the Sangheili Combat Form can, the Human Form has some advantages.

It seems to be more alert and is quicker to melee an opponent. It also presents a smaller, harder target to hit, especially the Infection Form, as it isn't protruding out of the body as much as those of Sangheili Forms. However, in Halo 3, the Human form becomes an easier target to hit; the Infection Form protrudes a lot more out of the host's chest and becomes a visibly significant target, and it seems to be significantly slower.



Sangheili (Elite) Form
The Sangheili Combat Form is a formidable enemy as it is very agile, resilient and capable of utilising 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 to hit.

In Halo 2, all of the Sangheili Forms encountered use one armor palette; the Minor Domo's Combat Harness. In Halo 3 however, the Sangheili Forms will retain its host's armor palette. Strength of each Sangheili Form will be dependant on the ranks of its host; an infected Sangheili Major will be considerably harder to kill than a Sangheili Minor.



Jiralhanae (Brute) Form
The Jiralhanae Combat Form, similar like the Sangheili Forms, is a formidable enemy and behaves more aggressively in combat than other Combat Forms as it will charge towards an opponent recklessly; this behavior is most likely as a result of the Jiralhanae's brutish nature and favor of close combat.

The Jiralhanae Form is more powerful than the Human Form but falls short under the Sangheili Form. It is bulkier and slower than other Combat Forms. Since the reanimation process strips the host of their damaged Jiralhanae Power Armor, the Jiralhanae Form cannot make use of their host's armor abilities.



Unggoy (Grunt) and Kig-yar (Jackal) Combat Forms
Although they do not appear in the trilogy, Unggoy and Kig-yar Combat Forms are introduced in Halo Wars. Their introduction is representative of the Flood's malleability - any creature of any type can be used by the Flood for its purposes.

Anti-Flood Countermeasures
Combat Forms can take extensive and sizeable amounts of damage before being neutralized. Arms, legs and even heads can be dismembered before they are incapacitated. The weak areas of a Combat Form are its sensory appendages that normally develop on the upper chest. This is where the Infection Form has nestled, and the body is incapacitated if this area is destroyed by a projectile weapon.

In all three Halo games, a Combat Form may fall only to stand up again and keep fighting. This can only happen if it still has a usable limb and appendage. In Halo 2 and Halo 3, if the body is not destroyed, Combat Forms can be revived by other Infection Forms crawling into it.

Human weapons are generally more effective against the Flood. Covenant plasma weaponry is designed to debilitate by causing burning pain and structural damage to bodies, but the Flood cannot feel pain or be crippled. In Halo 3, plasma-based weaponry and melee attacks, formerly weak against the Combat Forms in the previous prequels, are now highly effective. Piercing weapons such as the Sniper Rifle and the Beam Rifle have little effect on Combat Forms. At a distance, explosive ordnance such as grenades and ranged weapons such as the Battle Rifle or the Covenant Carbine can performs well against Combat Forms. Do note that Plasma or Spike grenades should be used with caution, as the Combat Form will sometimes ignore all other targets and charge players using those weapons at high speed. The Needler can be devastating, as the needle explosion will prevent it coming back to life in Halo: Combat Evolved, and will shatter it in Halo 2 and 3. In addition, the Needler's explosions will destroy an entire horde of charging Flood Combat Forms, similar to grenades and rocket launchers. For ranged weapons, it is recommended for players to focus their fire at the sensory appendages that is visible on the Combat Forms as successfully firing at one will immediately bring down a Combat Form. Dismemberment with ranged weapons is also recommended to prevent the Combat Forms from firing their held weapons. At close combat, it is recommended that the individual acquire close quarter weapons such as the Shotgun, Energy Sword and Gravity Hammer as they perform exceptionally well against Combat Forms. Burning the Combat Forms with sufficient amount is one of the most effective methods in any situation, as is destruction of the torso.

General

 * In Halo: Combat Evolved Combat Forms will not disintegrate from successive melee hits when they are dead like in Halo 2 and Halo 3.
 * Flood Combat Forms seem to take on physiological and biological changes throughout the Halo trilogy; these changes from game to game could be due to the Gravemind's influence in attempting to create a better Flood soldier or they could be simply graphical updates.

Halo: Combat Evolved

 * In all of the Halo games, Flood Combat Forms always hold the Shotgun with one hand, and fire it without pumping another round into the chamber. They somehow manage to make the shotgun pump itself. A possible explanation for this is that the Flood has extended an appendage into/onto the Shotgun which allows it to use the Shotgun's pump as a body part, or the pump action just wasn't programmed into Halo: Combat Evolved.
 * In Halo: Combat Evolved if you stand on a Light Bridge (343 Guilty Spark) and shoot off armed Combat Forms' gun arms, they will leap onto the bridge and get stuck and will only be able to move by jumping at you.
 * If you shoot both arms off a Combat Form in Halo: Combat Evolved it will not be able to attack you and will simply follow you around. Players have dubbed this instance as creating a "[[Flood Friends|Flood Buddy".
 * This is the only game in which an Infection Form cannot revive a dead Combat Form; instead there is a chance that the Combat Form will just get back up again.

Halo 2

 * Halo 2 is the only game where the Flood are able to drive vehicles.
 * When using the Grunt Birthday Party skull against the Flood in Halo 2, the effect of the skull will cause the plasma grenade explosion to occur when you shoot the Combat Form in the chest, where the Infection Form is.

Halo 3

 * The Combat Form can pick any weapon should it be near them when they "resurrect".
 * Sometimes, Flood will wield Flamethrowers if they are revived close to one. In some cases, they can be seen wielding Plasma Turrets with one arm or tentacle. This is common on the level The Covenant, right after you kill the Brute Chieftain with the Plasma Cannon. This may either mean that the Flood has built up a powerful muscular structure in the host during infection, or they haven't been programmed to hold these weapons with two hands.
 * An infected Jiralhanae Chieftain will turn into a Jiralhanae Combat Form with Jiralhanae Minor Power Armor on. These errors were due to memory constraints and also represent the rapid increase of visual effects technology over the course of the development of the games.
 * Regardless of gender, an infected Human Flood becomes a male Combat Form. There are no variations between an infected male or female Marine.