Flood pure form

"Alas, brother. The Flood... it has evolved!"

- Sangheili Commando

Pure Forms, also rendered pureforms, are an advanced type of Flood form. They are only available for the Gravemind to put together during the Coordinated Stage of Flood development, and are not created by infecting an alien host.

Overview
Unlike the more "conventional" Flood forms such as Combat and Carrier Forms, Pure Forms are not the product of infecting a sentient host, but are instead composed entirely of converted Flood biomass. Tissue from consumed victims is transformed into Flood Super Cells, which are then attached to a framework of recast bone modified for the Flood's purposes. The resulting Flood form is capable of mutating between 3 (possibly more) different forms depending upon the necessities of combat.

Pure Forms can only be produced when a Flood outbreak has amassed considerable amounts of biomass and formed a Gravemind. Once this threshold is reached, the Pure Forms provide combat support to the mainline Flood forms the Flood has at its disposal. As the parasite grows in strength the key minds begin to cultivate tumorous masses and mucus-like lakes of pure Flood cells using nonessential biomass as food. Most of the Flood cells are used to form hives and blightlands, but some is harvested to create deadly war-forms. With the sound of breaking bones and ripping flesh these creatures transform themselves to best confront the threats they encounter, contorting and reshaping their anatomy into grotesque but lethal shapes as they lead hordes of lesser combat forms into battle.

Stalker form
Stalker forms are extremely agile and can jump large distances. They tend to crawl on ceilings and walls before leaping at an opposing enemy. The Stalkers attack far more rarely than the other two forms. If threatened, it will transform into either a Tank or Ranged form. Their chesspiece role is to seek out enemies and then decide whether to transform into Ranged or Tank forms accordingly.

Ranged form
Ranged Forms can usually be found clinging to ceilings or walls, though unlike the Stalker Form, they cannot move from a given spot. They can fire sharp projectiles from a long range without the need of a weapon. These are slightly more tricky to kill due mainly to the fact that they can pin an enemy down in a position for a very long time. If they are left alone for some time, they will change back into a Stalker Form, get a better angle, and become a Ranged Form again. Their role as chesspiece is to pin down enemies with suppressing fire from afar so that the close-combat reliant flood forms can advance on the enemy undisturbed. They are to flood what machine gunners are to humans and Covenant as they lack the subtlety to be snipers, though they are just as accurate.

Tank form
Named for their immense endurance and strength, Tank Forms are the largest variety of Pure Form and are easily spotted from a distance. Unlike the other Flood Pure Forms, they can not climb on walls and ceilings due to not having a stealth background. These Flood can take a tremendous amount of damage and can kill you in one hit on higher difficulties. They also occasionally spew Infection Forms from their 'mouths'. It takes a long time to kill one with other weapons, but the Energy Sword can kill them in one hit. Their chesspiece role is close-ranged attacks to soften enemies up for infection.

Infester form
The Infester Form is a Pure Form that was created for combating the UNSC and the Banished on Installation 00 in 2559 after the Banished breached the remains of High Charity and released Flood forms still residing within. Its primary purpose is to break open vehicles and infest within in order to take control of them and expand the Flood's forces killing the Infester in the process. If an Infester cannot locate any vehicles then they will target any other non-Flood entity and attack.

Spawner form
Spawner Forms, like the Infester Form, were created to counter the threats on Installation 00. They seek out uninfected areas where they will create other Flood forms that will infest the area.

Production notes

 * The Flood Juggernaut, a Flood Form cut from Halo 2, was an early concept of the Halo 3 Pure Form. The Sharquoi, a deleted Covenant species from Halo 2, may have served as the inspiration for the Tank Form. This is further proven by a piece of concept art in The Art of Halo 3 that appears to be three Flood Juggernauts engaging several Marines and the Master Chief in combat.
 * If a Pure Form is stuck by either a Plasma Grenade or Spike Grenade while mutating, the grenade will be "absorbed" and no explosion will occur. In addition, if a player kills a Pure Form in the middle of transforming, it may appear with strange deformities. If a Ranged form is transforming to a Stalker and the player kills it, depending on when the player kills it, it can appear as a Ranged Form with a Stalker's feet or, more often, a Stalker with oversized feet.
 * A Tank Form is featured on the map Cold Storage in a cryo-container, but is partially dismembered and will occasionally twitch and spasm, suggesting that it may be under some sort of drug that neutralizes its hostility.

Cut Forms
"I think ultimately, we tried to do too much. One form that transformed three times to different sizes that had totally different functionalities was probably more than necessary."

- Shi Kai Wang

Infector form
The Infector is a three-limbed form that features the ability to regenerate destroyed limbs within ten seconds, making it a formidable foe. Their bodies are very similar in appearance to the Carrier Form, except that the infector form is designed to shoot out spores, not explode and release infection forms. It was cut from the final game.

Transport form
The Flood Transport Form was a Flood Purestrain form. Unlike the Carrier Form, the Transport carries up to six unarmed Combat Forms. It had four triple-jointed walking arms to move its load of troops around, and featured numerous tentacles to consume or recycle bio-mass. It was cut from the final game.

Stealth form
Like the Stalker Form, it excelled in the art of stealth to defeat the enemy. It was the only Pure Form to be able to use weapons with the aid of two four-tentacled hands. It was cut out from the final game.

List of appearances

 * Halo 3
 * Halo Legends
 * Origins
 * Halo: Combat Evolved Anniversary
 * Terminals
 * Halo 5: Guardians
 * Halo Wars 2
 * Halo: Fireteam Raven