The Flood

The parasitic organism known as the Flood come in 4 main forms Infection, Combat, Carrier, and Brain. Each Flood organism starts out as an Infection form and then once infecting the host proceeds down its lifecycle depending on which organism it took over and the organisms condition. The Flood are an Intelligent species and once consuming a host, gain access to all its memories. The Flood are very deadly and Spread very quickly. The Flood were what caused the Forerunner to construct the Halos and eventually activate them in hopes of stopping the Flood from spreading. The Flood that were loose on planets died off, having nothing to feed off of. However some of the Flood were contained in Forerunner facilities in stasis, just waiting to be released once again into the galaxy.

Infection form: The Infection form infects a host by inserting a needle like appendage into the host's spinal cord cutting the brain off from all control over the body's functions except for supporting functions such as breathing and heartbeat. Infection forms can jump reasonably far and can walk on any surface including walls so always watch your back. This form is physically weak and only a threat to unshielded soldiers or in large groups. Only 1 shot is required to destroy it, and when one is destroyed it makes a powerful pop, this resulting pop can destroy other nearby Infection forms. Infection forms will also pop when they hit a shielded object such as an Elite or Spartan's armor.

Combat form: This is what results when a Infection form infects a human host, a very strong and very dangerous killing machine. The human version of the Combat form is much smaller, weaker, and slower than the Elite version but can still jump the same distances. The Elite version of the Combat form is much stronger and is much taller than the Human version. The Combat form is still capable of using weapons and in the case of the human Combat form, prefers human weaponry over Covenant weapons, and the Elite version prefers to either attack with its whip like arm or using Covenant weapons. The Combat form in addition to using firearms also has a strong and deadly whip like protrusion on its arm that is made out of the hosts calcium reserves.

Carrier form: When a either an Human or Elite Combat form is too damaged to continue fighting it is transformed into a Carrier form, infected Grunts are also immediately turned into a carrier form since the Flood do not recognize them as an effective combat form. Once the conversion begins to take place the inside of the host swells up and future Infection forms begin to develop inside, the Carrier form will keep the Infection forms inside safe until they are ready to infect a host. When the Infection Forms are ready the Carrier form will go up to a host and fall over, then promptly explode showering Infection forms down onto the stunned host. This same result happens when an enemy approaches a Carrier form or if a Carrier form takes too much damage. Carrier forms are very slow because of the condition the hosts body is in, very often the hosts body integrity is very low and continues as the body's resources are increasingly consumed by both the Carrier form and the now growing Infection forms.

Brain form: This is the rarest and most helpless of all the Flood, it is immobile and has no way of defending itself, however it is guarded by all the other Flood forms. The only way a Brain form is created is when an Infection form infects a technician or a captain (such as Capt. Keyes). The Brain form, if the infected host is still alive, can pilot a ship or infiltrate a computer system. Flood Brain Form

Juggernaught: The Juggernaught is a unknown Flood type that has never been encountered before. The good folks at HBO (Halo.Bungie.Org) were kind enough to put a set of pictures up and even a video. Whether the "Juggernaught" was put there intentionally is not known and neither is whether Bungie plans on introducing it into the still unannounced Halo 3 (you know their gonna do it) here are the links to the other 2 pics, 1 and 3.

WTF!!!