Combat Form

A Combat Form is a vertebrate suitable for combat that has been infected with the Flood parasite via an Infection Form and mutated into a combat unit that fights for Flood goals and objectives.

Introduction
A combat form comes into existence when an infection form made of Flood super cells attaches itself to a lifeform with sufficient biomass and calcium store. It then uses a protruding neural connection to interact with the host's nervous system, synchronizing with it's electrochemical signals and gaining control over the host's body. It has been theorized that certain nervous disorders, such as Boren's Syndrome may counteract this effect and render an infection form harmless. During the infection process, the host's internal organs are liquified and the nutrients from them are used to develop the tentacles and other appendages of the combat form. Penetrating weaponry, such as the Sniper Rifle, have little effect on the Flood combat form because of this. The Flood combat form still has reliance on some of it's host's life support functions and as such any projectile or melee weapon with enough force to damage these systems can effectively kill the combat form. Unfortunately for the host, he/she stays alive for the duration of the transformation process and is even conscious and aware after the final transformation. 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. On rare occasions, this effect may be weakened by time in stasis, allowing the host to regain some control. These combat forms can use any and all knowledge previously attained by the host, and as such can wield weapons, as well as drive vehicles and board enemy vehicles.

Purpose
During the initial stage of a Flood Outbreak, the Feral stage, these forms communicate via pheromone-based communication and are used to secure new hosts for use as biomass and complex neurosystems to strengthen the local Gravemind. 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 relegated for use as either defensive units or additional calcium/biomass reserves.

Types of Combat Forms
Of the various races of the Covenant hegemony, there are only a specific amount of species that have the necessary requirements to become potential Flood vectors. Species known to be immune to infection include the Lekgolo, whose segmented neural structure make synchronization for the Flood form impossible, the Kig-yar whose avian bodies do not contain the necessary calcium stores, the Yanme'e whose chitinous shell makes infection impossible and the Huragok, whose artificial nature removes it's infection potential. While other forms of Flood Combat forms are conceivable, only three are seen during the span of the games.

Human Form
The human combat form is significantly smaller than other forms, due to the comparative differences of the host bodies. 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 try and fight. Although it cannot take in as much damage as the Elite combat form can, it has some advantages to its counterpart: it seems more alert, is quicker to melee an opponent, and presents a smaller, and thus harder to hit, target. Since they wield the weapons of former UNSC Marines, they can be deadly at any range. They are also capable of driving UNSC vehicles such as Warthogs and Scorpion Tanks

Elite Form
During infection, the Flood pushes the Elite's head backwards to create sufficient space for the infection form to reside. The Covenant combat form is a formidable enemy and it is capable of a deadly physical attacks using its whip-like tentacles. They also have the ability to wield both human and Covenant weapons. It is very fast, very strong, and can jump great distances and heights. Some Elite combat forms can still use their armor's Active Camouflage and Energy Shields. Fortunately for the player, because of Elite physiology, they are 'bigger' than the human form, therefore presenting a larger target.

Brute Form
Brute Combat Forms, while mutated similarly to human and Elite Combat Forms, behave much more aggressively in combat towards an opponent. During infection, the Infection Form burrows into their skulls and force the jaws apart to create a residual space. These creature seem to draw on their host's brutish nature and often forgo projectile weapons in favor of close combat. They usually wield Brute weapons such as the Spikers, Maulers, and even Gravity Hammers, as well as more traditional Covenant weaponry and human armaments. These creatures have not been seen controlling vehicles but it is possible since brutes are seen piloting Choppers.

Fighting a combat form
The combat forms can take extensive damage before being neutralized. Arms, legs, even heads can be totally blown off of their bodies before they are incapacitated. The only known weakness of a combat form is its sensory appendages that normally develop in the upper chest region. This is where the infection form has nestled, and once destroyed by a projectile weapon, the body is incapacitated. In all 3 Halo games, a combat form may fall, only to stand up again and keep fighting moments later. This can only happen if it still has a usable limb. In Halo 2 and 3, if the body is not destroyed, such as by an Energy Sword, Grenade or Brute Shot blade, combat forms can be "revived" by other infection forms crawling into it.

Explosives such as grenades, rocket launchers, and the Brute Shot can easily kill a combat form. But, one must be careful if using Plasma or Spike grenades, as the Combat Form will sometimes ignore all other targets and charge at you at high speed. In the games, the Flood combat form is more vulnerable to human weapons. The nature of the Covenant plasma weaponry means that it's normally debilitating nature by causing epidermal and subdermal damage is canceled out by the Flood's inability to feel pain or be crippled. However, the needler can be devastating, as the seven-needle explosion will prevent it coming back to life in Halo: Combat Evolved, and will shatter it in Halo 2 and 3. At close range the Shotgun and Energy Sword are the best weapon for killing combat forms. A shotgun blast at short range or sword lunge will take them out permanently with no chance of them reviving. This tactic works with the Mauler too, if you cannot find enough shotgun ammo. At close to medium ranges the M6C Magnum and SMG are also very effective against combat forms due their fast fire rate. The Sentinel Beam is also a effective weapon due to its continuous fire and burning capabilities. At longer ranges the BR55 Battle Rifle, Covenant Carbine, or the M6D work the best against Combat Forms (2 shots to the upper chest where the Flood infection form is). The Brute Spiker is also an effective anti-Flood weapon, as the melee can completely destroy a human or Elite combat form in one hit. Burning Flood forms is one of the most effective methods in any situation, and is often the desired method of eradication.

End of Flood Life Cycle
Eventually, a combat form will mutate into a carrier or pure form, regardless of damage, to perpetuate the Flood species. The combat form will prematurely transform into a carrier form or pure form if it takes enough damage and the combat form cannot function effectively. As a carrier, the host will basically become a walking incubator for more infection forms. When it turns into a pure form it will turn to either a stalker, range, or tank form.

Harmless Flood
In Halo: Combat Evolved it is possible to remove both limbs from a combat form, rendering it harmless. These forms will follow the player and "nestle" close to it in an attempt to attack. It is only necessary to remove the tentacled arm of the combat form if it is not carrying a weapon, however if it is both must be removed. These forms can be used as effective shields and will often charge Covenant enemies as a distraction. This bug is removed in Halo 2, where attempting such a feat by removing both arms will cause the infection form to leave the body in search of another. It is still possible to utilize the single arm removal if the combat form is not carrying a weapon. This method remains unusable in Halo 3.

Trivia

 * In all Halo games, Flood combat forms always hold the Shotgun with one hand, and fire it without pumping another round into the chamber. (And in the case of Halo 1, they somehow manage to make the shotgun pump itself.)
 * Sometimes Flood will wield flamethrowers in a normal game if they are revived very near one.
 * In Halo 2 and Halo 3, all Flood combat forms have more of the host's armor left on them such as chest plating and etc., however, they were almost naked in Halo: Combat Evolved.
 * In Halo 2, all the Flood infected Elites wear the armor of an Elite Minor, even on the Forerunner Gas Mine where the only Covenant Elites are the Spec-Ops, the Heretic Elites and the Arbiter. Even in the entire level, Quarantine Zone and the level Sacred Icon are there only Minor Elite Flood, where no Minor Elites were found. This is probably due to make it easy to generate combat forms. In Halo 3 however, say an Elite Ultra was infected, then the new combat form will still have the armor of an Ultra, but when killed the armor myseriously changes to that of a minor.
 * In Halo 3, a Chieftain getting infected will turn into a Brute combat form with Minor Brute Armor on.
 * Occasionally, if you throw a Plasma Grenade on a combat form it will charge at the player, ignoring any other non-Flood targets. But in Halo 3 they will jump away from the grenade.