Flood Friends

Summary
In Halo: Combat Evolved you were able to neutralize Flood forms and make them harmless. Called Flood 'Pets' or 'Buddies' these zombies would still try and follow you around and could then be used as shields, taking enemy fire while you crouch and shoot between their legs.

Walk Through
This can be done on any level with the Flood. It works particularly well with the Assault Rifle and Pistol, though the Plasma rifle or Plasma pistol is recommended seeing as they cause less damage. When you spot a Flood, shoot off its tentacled arm. On higher difficulties, you may also want to shoot off the Elite infected flood's head, as this may be used as a weapon from time to time. If they are carrying a weapon, shoot off their right arm as well. Only the left arm must be amputated, and on Human infected flood, the head poses no threat. The arm in which they hold a weapon is only dangerous if they have a gun. After taking off the left arm, and sometimes the head, the Flood are incapable of hurting you. The number of Flood buddies you can make is technically indefinite, however the game will begin to slow after 6-7 flood buddies are acquired(if you have a slow computer), and lags severely when more than a dozen are present(again, if you have a slow computer).

Halo 2
Unfortunately in Halo 2 the game designers changed the Flood attributes. So that once you shoot the arms off a Combat Form it will shortly pop into an Infection Form. However, by shooting the left arm of a Human flood that is not carrying a weapon, you can create a Halo 2 Flood buddy. Though these tend to push you around, they cannot damage you.

Also you can kill the flood you find and in some cases they'll come back to life. If they do, before they come back shoot off their arms. if it comes back it'll have no arms.

Halo 3
In Halo 3, it is possible to make an actual Flood buddy by shooting off the tentacled arm or appendage of an Elite or Brute Combat Form that is not carrying a Weapon. In order to shoot the elite combat form's arm off, its shield must be down. The Combat Form will charge at you but cannot harm you unless it pushes you off a ledge. If you are facing away, they will also attempt to "assassinate" you with an invisible tentacled arm. (This will only take down a quarter of your shields.) Also, if your flood "friends" attempt to follow you after their designated checkpoint, the infection forms will detach themselves from the combat forms (not destroying the form but merely turning it into a ragdoll) and will run in random directions, and popping shortly.

Related Links

 * Flood
 * Combat Form