The heresiarch is a boss enemy from Hexen that appears as a large demonic sorcerer with red skin, a tail, and black robes trimmed in gold and violet. Three mana container-like cubes circle his head. He makes a cameo at the end of The Dome of D'Sparil in Heretic and appears as an enemy at the end of two hubs: Heresiarch's Seminary, and Castle of Grief. In Hexen: Deathkings of the Dark Citadel, there is one at the beginning of the Constable's Gate hub and another in Chantry; finally, one appears in Castle of Pain while playing in single-player. He has 5000 hit points making him just as tough as Korax himself. The manual describes him as such:
The heresiarch can cast four different spells:
- create a barrier that makes him temporarily invincible to all attacks except the Cleric and Mage's fléchettes and that also deflects most projectiles;
- shoot a stream of purple fireballs in a weaving pattern;
- summon two bouncing fireballs that home in on the target;
- when his health is low, he can also summon dark bishops.
There are three cubes orbiting slightly above the heresiarch, and it is these cubes from which the heresiarch draws his power. The purple cube allows the heresiarch to cast the purple stream of projectiles and the homing fireballs. The blue cube allows the heresiarch to generate his reflective/invulnerability shield, and the green cube allows the heresiarch to summon dark bishops.
Baratus (the Fighter) has the highest level of challenge in killing the heresiarch when compared to the other classes, as Timon's Axe is the only weapon that can damage the heresiarch while the barrier is up. Parias (the Cleric) has the most success using the gas clouds spawned by his fléchettes, due to their pierce and high damage per second. For Daedolon (the Mage), the sapphire wand and Arc of Death are safe to fire upon the heresiarch as they are not reflected by the heresiarch's shield, albeit not piercing through it. An alternative strategy is to get up close to the heresiarch (preferrably with an Icon of the Defender and spam fléchettes, since they pierce through the heresiarch's shield and do decent damage.
When the heresiarch dies, the cubes will fall to the floor and bounce several times before exploding. The explosions are very powerful and the blast radius is much larger than is apparent from the explosion sprites. Extra danger comes from the fact that a player might mistake the cubes for mana containers.
The heresiarch only casts spells when the player is within his line of sight. This includes his shield spell, so it is possible to minimize the amount of time that the heresiarch's shield is active by the following strategy: when the heresiarch first enters battle, damage him as much as possible, e. g. with one's relic weapon, which should always be available by the time you face a heresiarch in stock Hexen/Deathkings. Do not use the Dark Servant, as it might provide the heresiarch with another target and foil the strategy. As soon as the heresiarch raises his shield, run and hide nearby but out of his line of sight and count to 30 (this approximates the amount of time it takes the shield to wear off fairly accurately). If the heresiarch begins to come into view before the shield is down, immediately retreat deeper into hiding. As soon as the count is up, though, rush out and damage the heresiarch as much as possible once again until he raises his shield, then repeat the process as needed to kill him. With this tactic, it is possible to prevent the otherwise annoying situation where the heresiarch starts casting a spell just before his shield wears off, choosing the shield spell to immediately restore his shield. As an added bonus, it also lets the player avoid suffering attack from the heresiarch during his invulnerable period (not counting pursuit by the possessed lava balls).
The heresiarch uses the cubes to cast his attacks, the heresiarch himself does not actually fire these, this is why he can still attack when he is in a pain state. If one were to create an actor with these cubes, the cubes would still fire, but the actor would just be doing what it normally does, unless it has the same attack states as the heresiarch.
Hexen monsters have six byte-sized fields for a special and five args, when the monster is slain the special is run with the given args. (This allows to have simple scripted events such as opening a door when a monster is killed, without having to use ACS.) However, the heresiarch uses its args to communicate with the cubes, so using them for a normal action special would not be reliable. Instead, when the heresiarch is killed, it will execute the script with its special number. For example, in Hub 4: Gibbet, the heresiarch met in single-player mode has a special of 20; when slain, instead of calling action 20 (Floor_LowerByValue), it runs this map's script 20.
The IWADs contain the following numbers of heresiarchs per skill level:
- The heresiarch which appears at the end of Heretic's The Dome of D'Sparil episode has led some to believe that the heresiarch was the original design for Korax. That some wall textures depicting Korax also bear a stronger resemblance to the heresiarch strengthens this notion.
- The heresiarch is referred to as the "sorcerer" in Hexen's game data and source code, which can be deduced from the shortened variants "SOR" (for audio lumps) and "SORC" (for graphics lumps), and the enumeration constant MT_SORCBOSS in the source. This provides further evidence for the above case, as D'Sparil was referred to similarly in Heretic's game data.
- The heresiarch's sight and active sounds appear to be the phrases "my sacrifice" and "your weakness" reversed and put through a filter.
- Various (23 December 2011). Doomworld Forums. Retrieved 3 September 2018. .