From Halopedia, the Halo wiki
The Pod infector is one of the easiest creatures to eliminate in the Halo series, requiring only one shot from any weapon. However, as easy as it may seem, a swarm of infection forms can also be a formidable threat to the unwary individual.
In order to overwhelm hosts, infection forms attack in large swarms, leaping at any nearby targets and attacking with their claws and tentacles. If the victim's shields are active, as explained earlier, the infection form will burst. However, the sheer force of numbers can sometimes deplete a victim's shields, allowing these Flood forms to take control of the host's body.
While individual infection forms are weak, in large numbers they can exert a surprisingly powerful force, being able to shatter doors made of Forerunner alloys.
A single round from any weapon will burst an infection form. For this reason, automatic weapons are recommended. Dual-wielding Okarda'phaa-pattern plasma rifles, Brute Plasma Rifles, Spikers or using a UNSC ballistic weapon all work well. The Battle Rifle with its bursts fire can be quite effective and the Shotgun can work well too when shooting at large groups closing in. Try to avoid using weapons such as M6 Handguns, as their rate of fire is very low. Also, try to use Grenades, but be careful as sometimes Infection Forms can be stuck with Anskum-pattern plasma grenades and may harm you when it gets close. In Halo: Combat Evolved, automatic weapons like the Assault Rifle and Okarda'phaa-pattern plasma rifle are good on them as well as the Plasma Pistol, and the Needler can turn out to be a very good alternative as the needles have homing ability. Be careful though, do not stick too many Needles on one at a time while they are close as if you do it will explode and effect you most likely depleting your shields. The best way of using it is to fire a single shot at each Infection Form, which is enough to kill them. SMGs are incredibly effective for taking on swarms of infection forms with its large magazine size and impressive rate of fire. The Sentinel Beam is also extremely effective and can swiftly obliterate entire swarms of infection forms at long ranged distances.
Infection forms are spawned from bulging, sac-like pods in Flood hives, called Flood blisters. It may be tempting to destroy these sacs, but it is actually more advisable not to, since destroying them will not kill the infection forms inside.
Halo: Combat Evolved
- It is best to leave the infection forms for last and focus on larger threat such as the combat forms and the carrier forms. However, it is best to focus on infection forms first if you bring allies with you, to prevent them from becoming infected.
- Shooting a swarm of infection forms can set off a chain reaction killing a couple of nearby infection forms within that swarm. For example, in a swarm of three infection forms, killing one could incidentally kill off the other two if they're close to one another.
- An Assault Rifle is the best tool to kill of a swarm, followed by the Plasma Pistol and the Needler (to kill one at a distance). Reserve the rest of the weapons for the combat forms.
- The Assault Rifle is the best gun. Additional ammunition is plentiful in the Flood campaign levels. Make full use of it.
- The Needler is fun to use on the infection forms from a distance. The homing needles makes it easier for the player to not aim properly and escape at ease.
- If all else fails, melee the infection forms.
- Unlike in Halo: Combat Evolved above, there is no "chain reaction" effect when shooting a swarm of infection forms. As such, the player must use considerable effort to kill the swarm. An SMG would generally be sufficient for such job.
- Similarly to the above section, it is harder (and potentially impossible) to melee the infection forms. As such, engage them at a distance.
- Much of the gameplay tips in Halo 2 section above can be used in Halo 3.
- The SMG and the Assault Rifle are the best tool to kill of the infection forms due to their ammunition count.
- Fire weapons, like the Orgudam Workshop firebombs and the flamethrower, are very effective against the infection forms.
- The Gravity Hammer is very effective against large groups of Infection Forms.
- Once an area has been mostly cleared of hostiles (enough to establish a Checkpoint), any remaining Infection Forms will usually explode if they have not found a body to infect.
- The Pod infector cannot re-infect Marines, Elites, and Jiralhanae that were killed in the middle of transforming into Combat Forms.
- Infection Forms function in a similar way to the infantry units of the other two races in Halo Wars; as damage is dealt, individual infection forms will die. They are also the weakest of the different forms.
- Unsurprisingly, it is a bad idea to engage Infection Forms using infantry. They can infect and turn your units against you (especially on higher difficulties) instead, deploy vehicles, particularly Hornets, as their airborne state makes them completely immune to all damage from Infection Forms.
- During the first encounter with the Flood in Halo War's Campaign (Ander's Signal), engage the different pockets of Flood forces using only your hero units; none of them can be infected, and Alice-130's chaingun is spectacularly effective at ripping through entire waves of Infection Forms
- Flame mortar-armed turrets are an excellent way to defend your base. Two medium turrets can hold off practically any infection form assault.
- When it infects an infantry unit (except for Hero Units), one of the squad will immediately leave the squad with health capped to 1 during the process and become an individual Flood Combat Form Unit with full health, regardless of any infantry squad type. Infantry units can be wiped out more quickly due to instant infection upon contact.
- When it infects infantry units, the infected infantry will gain invulnerability until the process to become Individual Flood Combat Form is completed.
- A Hero Unit can be instantly downed regardless of remaining HP when their shield is down.
Halo: Spartan Assault
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Halo Wars 2
- Units that deal splash damage are highly effective against swarms of infection forms. They can be easily killed with one splash shot. Hunters, Kodiaks and other such units are recommended to deal with Infection forms.
- Infantry will not be infected immediately upon contact; instead, a unit on the squad must be dying to start the infection process. This gives infantry a chance at fighting back hordes of Pod Infectors or fleeing from them.
- Garrisoned infantry will immediately leave the garrison upon infection.
- Turret defenses are no longer efficient at destroying packs of infection forms, even with anti-infantry upgrades and fully upgraded base fortifications, with the exception of the Siege Turret, Mega Turret and any defenses that deal splash damage.
- Similar to Halo Wars, they cannot attack air units.
- Beware of the Flood Swarmer, it can produce pod infectors on the spot.
- Pod Infestors and Seeder Infectors are new types of Pod Infector.
- The Pod Infestor specializes in infecting vehicles.
- Seeder Infectors specialized in infecting air units.
- Super Units cannot be infected.