Flood San 'Shyuum Form

Prophet Form is a term fans have created to describe the Covenant Prophets that have been infected and overtaken by the Flood. Due to their unusual nature, they are not thought of as Combat Forms in the way infected Humans, Brutes, Elites, Jackals, and Grunts are.

It is also worth noting that all "Prophet Forms" seen had only just been infected, and may not have been assimilated in the conventional way. The only Prophets to be seen being infected by an Infection Form were two of the three Prophet Hierarchs: Mercy and Truth. However, the Master Chief removed the Infection Form from Mercy, killing him, and Truth was killed by the Arbiter in Halo 3 before the Infection Form could complete the infection process. The Prophet of Regret became one with the Gravemind.

Appearance
The Prophet Form maintains the same general form of a Prophet, but with the decayed skin and appearance of a standard Flood organism. If they have been assimilated by Infection Forms, the form does not show visibly, as their sensory stalks do not protrude from the Prophet. This does not mean that the Prophet is kept completely intact; the assimilated Prophet of Regret had only a single, malformed arm, and was impaled by one of the Gravemind's large tentacles. Also, a Human skull can be seen in the top right corner of the Prophet Form, which is probably a part of another assimilated being.

It is highly possible that following the infestation of High Charity, more Prophet forms were created.

Similarities and Differences


The biggest difference between the Prophet Form and that of the conventional Combat Form, is that Prophet Forms seen thus far have maintained their personalities to an extent. Combat Forms are subjected completely, to the control of the Infection Form within them and generally display none of the former personality traits of their hosts. On the other hand, infected Prophets have demonstrated the ability to act the same way that they did before they were assimilated. As the Prophet species are considerably weaker and more frail than many other Covenant species, the Prophet would not be a suitable creature to create a Combat Form.

It seems, that they can operate as part of a Brain Form, as the Prophet of Regret appeared to be physically attached to the Gravemind. In the case that there is no Brain Form present, the Prophet Form appears to act, to an extent, as the leader of the Flood within an area, as seen with the Minister of Etiology. Along with that, they are the only Flood forms who, after being infected, can still talk (with the exception of Wallace A. Jenkins).

A skull can be seen in the top left corner of the Prophet Form. Looking just below the "Prophet Form" the hand of an Elite can be seen as well. In this sense, they are very similar to Brain Forms in that they are now chimeras of multiple species and individuals.

Personality
Four Prophet Forms have been encountered in the Halo universe, each having radically different personalities. The Prophet of Regret, after being infected by the Flood, appeared to maintain his previous personality, almost oblivious to the fact that he had been assimilated. This could be either because he was still partially alive, or because the Gravemind was merely controlling him like a puppet.

The Minister of Etiology, on the other hand, was completely unlike his previous self. He acted as a spokesperson for the Flood, even taunting Rtas 'Vadum by asking him what chance he had of defeating them when the Forerunners were utterly incapable of doing so.

The Prophet of Mercy had just been attacked by an Infection Form when he was shown, and the Infection Form was still in the process of converting him into a Flood Form when it was removed. As a result, his case cannot be taken as evidence of the behavior or appearance of Prophet Forms.

The partially infected Prophet of Truth seen in Halo 3, seems to have both retained his personality and acted as a spokesperson for the Gravemind. However, he appeared to be fighting the infection and had just been infected when this occurred, so his behavior and appearance may not be representative of infected Prophets as a whole.

These personalities may be related to the command structure of the Flood in the area. In Regret's and Truth's case, they were only a part of a larger intelligence, the Gravemind, so their personality did not need altering. The Legate on the other hand, appeared to be the controlling intelligence of the local Flood because the Brain Form on the ship had been destroyed and therefore his mentality was Flood based.

Trivia

 * It is unknown what happened to the body of the Prophet of Mercy, but it has been speculated that he was transformed into a Prophet Flood Form like the Prophet of Regret was (based on the Gravemind's response to Truth on High Charity: "We Exist together now, two corpses in one grave") or taken for biomass.
 * All three High Prophets during the Age of Reclamation were infected at one point.