The Flood are one of the most pervasive and dangerous enemies the player faces in the Halo series. Capable of infecting all living matter at a juggernaut’s pace, they seek to infect, mutate, and dominate all life in the galaxy.

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By process of evolution, mutations in various life forms, and the tweaking of the Gravemind, the Flood has developed a number of different forms. Each serve a vital role in the effort to transform the galaxy with some being stronger than  others.

24 Spores

Halo Flood Spore

The most basic form of Flood, Spores are miniscule organisms that are capable of infecting and suffocating living beings. These aren’t typically used by the Flood to create new hosts, but they have proven useful.

Any being that inhales the spores will suffer a slow mutation process that does not manifest as much externally. It’s less effective compared to other infection methods, though the Flood will sometimes disperse spores atmospherically to assist their efforts.

23 Tadpoles

Halo Flood Tadpole

These little guys appear in Halo 2 exclusively. They’re a less mature stage of Pod Infectors being smaller and are only seen in a tanks in a research lab. It’s unclear what their capabilities are, if any, thought it’s likely they serve a similar function to Pod Infectors.

22 Pod Infectors

Halo Pod Infector

Pod Infectors are by far the most common form in existence and are responsible for infecting other life forms. These small squid-like beings swarm over opponents until they can penetrate the victim’s flesh and wrap around the spinal column.

It then begins spawning Flood Super Cells inside the host and rapidly mutates them into a desired form of Flood. In large numbers they can be very dangerous, but individually they are little more than a nuisance.

21 Seeder Infectors

Halo Seeder Infector

Seeder Infectors are similar to Pod Infectors in that they infect other organisms and quickly transform them. The difference, and what makes them a little more dangerous, is that they are airborne. They can also spit out bone fragments of their victims as a weapon.

20 Carrier Form

Halo Carrier Form

Carriers are charged with spawning more Pod Infectors and keeping them safe during delivery. They will seek out life forms, explode, and simultaneously emit Pod Infectors to swarm the now weakened target.

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They’re slow and function as little more than mobile incubators. But in close proximity they are a major threat.

19 Burster

Halo Flood Burster

The Burster is similar to the Carrier in that it transports Pod Infectors and Spores into battle before detonating upon an enemy. The main difference, and why they’re more dangerous, is that they burrow underground before emerging and exploding.

18 Flood Swarm

Halo Flood Swarm

These are birds, bats, and other airborne animals that have been infected. The Flood Swarm travels in groups to overwhelm opponents with sharp projectiles. They are very weak and a single Swarm is hardly a threat, but in a cluster they are a nightmare.

17 Spawner Form

Halo Wars 2 Spawner Form

Spawners are essentially the Flood troop transport. They sit on the edges of battle spawning an endless wave of Pod Infectors. When their life is threatened they’ll spawn a unit meant to counter that threat. This allows them to keep sending waves of mini enemies and have the means to keep themselves alive.

16 Unggoy Form

Halo Unggoy Infected

These are Flood that have infected the Unggoy troops. These combat units are small and are similar to their hosts in that they’re cannon fodder for the Flood. The Flood rarely uses them in battle, instead having them act as the raw biomass for the Gravemind’s purposes.

15 Kig-Yar Form

Halo Kig-Yar Infected

Kig-Yar are similar to the Unggoy in that they’re small combat units rarely seen in actual combat. They are slightly more dangerous than an Unggoy as they will often still carry their Rifles, making them a ranged threat.

14 Stalker Form

Halo Stalker Form

Stalkers are made up of pure biomatter and their specialty is to find safe locations to mutate into a greater form. In combat they are fast and capable of leaping great distances. They’re also incredible fragile, capable of being destroyed in a single shotgun blast.

13 Human Form

Halo Human Infected

The Human Form is a dangerous combat form due to it’s small size and agility. They can be found wielding pistols, rifles, shotguns, and even rocket launchers. When out of ammo they will rush opponents and engage in melee combat.

12 Ranged Form

Halo Ranged Form

This pure form is essentially an organic turret capable of firing bone spikes at long distances.

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Removing a cluster of these is very difficult and they are very dangerous. The only reason they don’t rank higher is they are immobile.

11 Thrasher Form

Halo Thrasher Form

These are large ape-like creatures that have become infected. They ram into targets and slash out with the front limbs. Its not a common Form and the Flood seems to prefer other Forms to expend biomass on.

10 Jiralhanae Form

Halo Jiralhanae Form

When the savage Brutes are infected they retain their ferocity and aggressive nature. They will charged opponents and engage in close combat. They do not have armor and are less likely to hold weapons, making them brash frontline fighters.

9 Tank Form

Halo 3 Tank Form

The Tank Form is the most powerful that the Stalker can transform into. It’s comprised entirely of raw biomass and are tough to take down. It’s slow, but it can take significant damage and deal quite the blow.

8 Sangheili Form

Halo Sangheili Form

Sangheili Forms are dangerous as they retain many of the host’s combat abilities such as camouflage and energy shielding. They’re also fast, resilient to damage, and can wield a variety of plasma-based weapons.

7 Spartan Form

Halo Spartan Infected

The Spartan Form is by far the most dangerous infected lifeform seen in Infection multiplayer. They possess an organic sword for a left-hand, armor plating, and energy shielding. It’s a terrifying foe and the Spartan is the strongest of the Combat Forms.

6 Bomber Form

Halo Wars Flood Bomber

Seen in Halo Wars, the Bomber form is an aerial unit that drops Flood blisters which erupt to spew Pod Infectors. They’re very effective in combat and carefully aimed drops can cause havoc on the battlefield.

5 Infester

Halo Flood Infestor

The Infester is a form of the Flood that appeared in Halo Wars 2. It’s capable of latching onto vehicles carrying personnel and infecting everyone in one swoop. These infected beings are fused with the vehicle making it a terrifying machine of war.