Phoenix Logs/Flood Lore
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The great devourer.
The Flood is a voracious hive-mind parasite that seizes, converts, and controls sentient hosts to perpetuate itself. Infected individuals have their nervous systems suborned by the parasite, turning their bodies into puppets while their memories and flesh are assimilated and exploited to further the infestation.
Each infected host is linked to a distributed intelligence, allowing for interstellar coordination and the formation of increasingly sophisticated consciousness nodes. If the Flood is not stopped it will eventually manifest a malevolent meta-intelligence known as Gravemind.
Flood are composed of a highly adaptable and resilient neuron-like "super cell" that has no analogous structures with other life in the galaxy. These protean cells are the building blocks of all Flood and can be configured into any shape or pseudo-organ necessary to sustain the biological and organizational growth of the parasite.
Encysted Flood cells form spores which can parasitize both sentient and non-sentient species, rapidly consuming the host and transforming their biomass into an incubator for larger, more mobile Flood combat and infection forms. There is no inoculation against infection, no treatment to slow the parasites' growth, no reversal of its transformation. The only effective countermeasure is containment and incineration.
A nightmare tide rises.
Flood infection forms are nightmarish homunculi spawned in massive numbers for the singular purpose of converting all living creatures into carriers, tools, and food for the parasite. The most commonly encountered infection forms have soft, pod-like bodies with numerous tentacle-like appendages and a frond-like array which acts as the creature's sensory system. Their tendrils are multi-purpose locomotion systems and insidious methods of control.
Each tendril ends in nano-scale barbs which can latch onto the target's body and cut through armor or environmental suits. Once the target is compromised, infection forms inject Flood cells to hijack the victim's nervous system. Even if the infection form is quickly removed, Flood cells in the wounds will slowly consume the victim and turn them into quivering, spore-packed blisters. Against unprepared victims the infection form bores into the body, quickly mutating it into a combat form.
Though barely intelligent on their own, once an infection form infiltrates a sentient creature they turn the victim's cognitive power to the furtherance of Flood goals. Each is an insidious puppeteer, able to sift through memories of any sentient creature to learn of military countermeasures, security access codes, and the location of population centers. This information is then shared with other Flood through their connection with the key minds.
Combat forms are relatively intact sentient hosts under the control of an infection form that has nested within. Though sections of the host's body are consumed and converted into Flood cells, some limbs and sensory organs are retained to utilize available weapons, tools, vehicles, equipment, and even starships. The infection form does augment its new body and repair minor damage in order to better serve as a living weapon, but ultimately the combat form is utterly disposable.
The infection form driving the host body does not feel pain or fear, though the same cannot be said for the host. Worse, in some horrific circumstances the infection form is unable to completely dominate the original personality and the victim remains fully aware of their irrevocable transformation and use as a tool of the parasite.
The Flood can survive and grow in almost any environment, but it thrives in a surprisingly narrow band of habitability. The interior of Flood hives provide a controlled environment for accelerated growth, but in time an entire planet's biosphere can be altered to approximate these ideal conditions.
Blightlands are the first step of this coversion process: areas around established hives filled with specialized Flood growths which harvest the vitality of the soil, soak up solar energy, and consume all native life within its boundaries. While they briefly flower with a grotesque vitality, ultimately these zones are themselves consumed to provide raw materials for city-sized spore towers and colossal stacks of strange Flood organs that finish the planet's ruination.
Bone and bile.
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.
Fonts of malign intelligence.
After an infestation is established the parasite transitions from feral aggression to coordinated conversion by creating specialised Flood organisms that network their individual intelligences. These key minds act as coordinators for nearby Flood, leveraging wisdom harvested from the parasite's hosts to expand, outwit, overwhelm, and consume other life.
As the Flood grow in number these key minds combine and expand into larger, exponentially more intelligent networks. The appearance of these vile collectives typically indicate most local animal life and sentient hosts have been infected or consumed. Once a critical mass of key minds have combined the Flood's centralized intelligence can begin to emerge in their seething mass of corrupted flesh: a Proto-Gravemind that sifts through and feeds on the memories of every Flood-infected victim.
High Charity's Bane.
The Proto-Gravemind within High Charity is the shadow of a far greater threat, one that will unleash damnation upon the stars should it grow unchecked. High Charity's proto-Gravemind is a perverse mockery of a living thing, a gluttonous stump of Flood cells that remained behind when Halo's cleansing energies burned away the corrupted biomass which once supported the Gravemind.
A measure of Gravemind's intellect remains, though its new vessel must feed and spread in order for it to manifest fully once again. With every Banished soldier that succumbs to its embrace, the Gravemind's re-emergence grows closer. The mountain of half-dead flesh quivers in anticipation, and the echo of timeless laughter rises from somewhere deep below.
High Charity's Proto-Gravemind is a massive, highly adaptable biological weapon. It is a horrifying enemy, protected by every Flood beast on the Ark. Only fools and madmen dare to attack it without overwhelming force.
A single intelligence inhabiting multiple instances.
A Gravemind is the apex of the Flood's coordinating intelligences. It is a monument of ancient sins; a self-aware compound mind that transcends individual hosts and lesser key minds; a formless intellect who knows all that the Flood have ever possessed.
The Gravemind brings its horrific form of peace through unification, salvation through assimilation. Its only goal is the consumption of every thinking creature in the galaxy. The Gravemind's most recent physical avatar was destroyed when the Master Chief fired the Ark's incomplete Halo, but it is only a matter of time before it rises again.