Heretic Sangheili are Covenant Sangheili that rebelled against the Covenant's High Council during the events prior to the discovery of the second Halo ring.
Heretic Sangheili encountered in Halo 2 are the Sangheilis of the artifact retrieval group led by Sesa 'Refumee. When 'Refumee discovered the truth about the Halos, his Elites followed him in the rebellion against the High Prophets, knowing what the Halo Installations would do if they continued The Great Journey. They used the Gas Mine above Threshold as a base, and placed Banshees and at least one Seraphs starfighter as an "Air Force" to defend the mine. They also set up a makeshift camp on Basis, Threshold's moon.
This camp is a playable multiplayer map, called Burial Mounds.
They do what they can to stand out to the rest Covenant, especially Elites.
They have a limited Rank System, consisting of:
■Heretic Sangheili Minors
■Heretic Sangheili Majors
Heretic Sangheili do not wear combat helmets like their Covenant counterparts do, but instead don breathing apparatus to assist in respiration on the Gas Mining facility. Heretic Sangheili also have four fins on the back of their armor, similar to the traditional armor seen on Ripa 'Moramee's clan brothers in Halo Wars: Genesis. The Heretic Leader Sesa 'Refumee does not share these fins, but instead has a jet pack on his back nearly identical to those used by Ranger Elites.
Heretic Elites can be found in both brown and gold armored variants, as well as the Heretic Leader's personal red-colored armor. Sangheili who wear gold armor are the equivalent of Elite Majors with more health and stronger shields, while those with brown armor seem similar to Elite Minors.
They are only seen in two levels: The Arbiter and The Oracle
They mostly use Carbines, Sentinel Beam, and also Energy Swords, but are never seen using Plasma Grenades. Plasma Rifles are only used by Heretic Banshee pilots and the Heretic leader. This most likely originates from the fact that the Heretics want to shun the Prophet-given plasma weapons and further themselves from the Covenant's Great Journey.
The energy shields of the Gold Heretics are as strong as a Majors, while the energy shields of the brown ones are as strong as a Minors. Note that their shields glow purple instead of the blue that Covenant-loyal Sangheili use
The Leader
Sesa 'Refumee was the leader of the Heretics, referred to in Halo 2 as simply the Heretic Leader, who had taken control of the Gas Mine on Threshold and a small base on Basis, the gas giant's moon which Installation 04 rests between. Concurrently with the Prophet of Regret, Sesa 'Refumee is the main antagonist for the first half of Halo 2, specifically for Thel 'Vadamee's first section of the campaign.
Sesa 'Refumee commanded an Artifact Retrieval Group attached to the Covenant fleet at the first discovered Halo ring, Installation 04. Early in the battle, a Minor Prophet ordered 'Refumee's detachment to investigate a Forerunner mining facility in the upper atmosphere of the gas giant Threshold. 'Refumee's commanding officer, Thel 'Vadamee disapproved of the action, and ordered that the rest of the Covenant military forces engage the humans.
Due to this, he was fortunate enough not to be on the Ringworld when the Master Chief destroyed it. Sesa 'Refumee first encountered Installation 04's Monitor, 343 Guilty Spark, a few days after the Halo’s destruction. The Monitor told him of the true nature of Halo, the fate of the Forerunners, and the origins of the Flood. This knowledge inspired 'Refumee and the Sangheili and Unggoy under his command to revolt against the Prophets. He also began to preach the truth to other Elites and Grunts in hopes that others would rally to their cause, which infuriated the High Prophet, Truth.
Sesa was branded a traitor and Heretic by Truth, who sent the new Arbiter to execute 'Refumee. At first, 'Refumee tried to protect himself by releasing the Flood in specific areas to kill the Arbiter and his strike team in the Gas Station, as a perilous and lethal storm raged outside. To force 'Refumee out of hiding, Thel cut the cable that prevented the station from falling into the gas giant. As he attempted to make his escape in a Seraph fighter, Thel found him and engaged him in battle. Despite his clever use of Holo-Drones, the Arbiter successfully dispatched 'Refumee and retrieved the Oracle from the station.
With the death of the Heretic Leader and most of his followers at the hands of the Arbiter, 343 Guilty Spark in the hands of Tartarus and the Hierarchs, the Heresy was quelled. However, its ideals were later revived during the Great Schism by the Covenant Separatists.
For all intents and purposes, Sesa 'Refumee, on his own, is just a Sangheili Ranger with differently-colored armor and shields that could withstand up to two Energy Sword lunges, making him accurately comparable to an Ultra Elite. He utilizes two Holo-Drones to assist him in a fight and as a method to stay away from harm's reach. These Holo-Drones, when projected, creates two identical models (albeit a darker armor tint) of himself, which deal real damage upon the player. When a Holo-Drone is "killed", the model will dissipate and the Holo-Drone ball will simply drop to the floor. On higher levels, defeating the first drones will make the real Sesa fly into one of the pipes and several more drones will appear. However, the real Sesa will often hide in one of the pipes on the top of the room. He will not respond to damage and can be easily killed with a Carbine or Needler.
