Tripartite Worship of a Chaos Entity
The Thanatar cult is an oddity in modern Glorantha. An attempt to revere a Chaos entity lost in the Gods War, it is a syncretism of different magical groups. Some blame its resurgence on the sort of magical meddling that backfired on the God Learners; others say the Lunars, Shamans, or Sorcerers are to blame. As the Thanatari are extraordinarily secretive and their works are routinely burned when found, the truth may never be known.
    What is clear, however, is that the combination of groups provided complementary abilities and services that have created a greater threat than the individual parts were before. Scholars of the Horned Society are reputed to have helped Than practitioners perfect their gruesome head-creation rituals. Than assassins have been found to be using Tien feats in their attacks, and so on. Truly, three separate nightmares have combined to form a looming disaster. The threat is great enough that even normally-hostile groups, such as Sartarites and Lunars, sometimes team up when a temple is discovered to eradicate all traces of Thanatari.

Entry Requirements: Prospective members must convince an existing member of their worthiness and sincerity. Many require bribes of lore or money before they will admit new members. Since the whole organization is persecuted and hunted, even finding someone to admit them is a challenge for non-chaotics.
Abilities: Chaos Lore, Worship Thanatar.
Virtues: Secretive.
Core Elements: The organization consists of three subgroups: the Horned Society (which reveres Atyar as the Devourer of Knowledge), the Than Practice (which worships Than as the Headless Spirit), and the cult of Tien the Severed God.
Magic: Members receive their magic from their subgroup. Despite being members of either a wizardry school, a spiritual practice, or a theistic cult, Thanatari can read grimoires from the Horned Society as if they were students, gain charms from the Than Practice as if they were spiritists, or learn affinities from Thanatar as if they were initiates without penalty. Such is the nature of Chaos.
Great Secret: None.
Other Side: Thanatar’s worshippers go to the Place of Waiting, which has connections to the God World, the Spirit World, and Essence Planes. The Place of Waiting is reputed to be that part of the Underworld where Tien was beheaded. Chaos brings marvels and terrors alike.
Disadvantages: Worshippers may never use fire or light abilities, even if those powers are stolen. Their propensity for attacking members of other groups and stealing their secrets has left the group hated and feared by all others.
        The Thanatar religion is rife with internal politics. Adherents constantly labor under the threat of assassination for posing a threat to a rival, suffering censure for being allied to someone who poses a political threat to an elite, being sent on a suicide mission to aid the cause of other Thanatari, being manipulated into becoming a scapegoat for a rival, and so on. Many of the Secrets of the religion benefit from ritual support but little support can be gathered. Why aid someone who will later become a roadblock on your own path to power? Loyalty is rare among the Thanatari.

The Horned Society
School of the Horned Skull
The Horned Society is a scourge that has operated in secret for centuries. Established by a rogue priest of Lhankor Mhy named Treack Markhor, this sorcery school is dedicated to the theft of magical secrets. The sage discovered a horned skull worshipped as a spirit of death on an unnamed island. Intrigued by the power he sensed within he took the skull with him, keeping it secret from his brother sages. Through decades of study he unlocked its secrets, naming the skull Atyar, Devourer of Knowledge. He drew a number of like-minded individuals into his service, and they formed a secret society.
    The group began stealing magic from other groups, first targeting small, outsider cults and other secret societies. Eventually their hunger for knowledge grew too powerful and more prominent religions and churches were plundered. The authorities moved to purge the group. The senior members of the Horned Society met one more time in its secret underground sanctum and secured the skull of Atyar in a vault protected by the most powerful magics they had—their own powers and those stolen from others. Then the Society broke up and went out into the world.
    The Horned Society operates in cells, usually composed of two to four adepts, supported by about two to three times as many apprentices. Individual members hoard their stolen knowledge, loathe to trade even the simplest magic except for a greater power. Members steal from each other as well as others. The Portal of Power created by adepts of the Horned Society is the Entropic Equation.

Abilities: Create Portal of Power, Focused Will, Read [Language], Rule of Treack Markhor, Symbolic Sight, Write [Language].
Relationships: Member of [Horned Society Cell].
Virtues: Hate Truth Gods, Paranoid.
Grimoires:
[Truth] Feast of Forgotten Lore (Confuse Foe, Decode Grimoire, Devour Book, Frighten Mortal, Ingest Scroll, Recognize Secrets, Sense Learning, Transfer Thoughts [D+20 to steal mundane secrets])
[Chaos] Gospel of Atyar (Absorb Feat, Dismay Victim, Dissect Spell, Inspire Zealotry, Prophetic Voice of Atyar [D+20], Summon Essence of Teaching, Unravel Charm)
School Secret Requirements: Chaos Lore 1W2, Use Feast of Forgotten Lore 1W2, Use Gospel of Atyar 1W2.
Secret: Consume Mind ritual (Chaos magic. The adept attempts to consume the mind of a helpless individual, in a ritual held over the course of Truth week in any season. It does not work on devotees or disciples of Lhankor Mhy. The ritual is dangerous and risky, and most Atyari only conduct it in their most secret of sanctums. Use of the ritual results in you receiving a chaos feature.)

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Contest: Consume Mind
Appropriate Ability: Consume Mind ritual Secret.
Typical Modifiers and Augments: Focused Will; ritual magic.
Resistance: The target’s best ability, even if it does not seem appropriate.
Any Victory: The victim is dead. You may spend 1 hero point to start a Memories of [Victim] ability at 13, +1 per additional hero point spent. This ability may be used to augment relevant abilities, and you may also learn any of the victim’s mundane abilities that you do not currently possess to the level of the victim, spending hero points as usual. You are also Impaired.
        If the victim was a theist, you may pay 6 hero points to gain one of the victim’s affinities at 13, +2 for each mastery the victim possessed in that affinity. If the victim had learned feats in that affinity, you also gain one of them for free; other feats from that affinity that were known to the victim may be acquired at the cost of 2 hero points each.
        If the victim was an animist, you may pay 2 hero points each to gain the target’s Friendship with [Spirit] abilities at 13, +2 for each mastery the victim possessed in that ability. You may create charms and fetishes for spirits possessed by the victim by using your Rule of Treack Markhor ability in place of Follower of [Majestic Spirit] or Worship [Great Spirit]; you always pay the “Not Concentrated” cost in hero points (see HeroQuest page 141).
        If the victim used wizardry, you may spend 6 hero points to gain one Use [Scripture], Use [Formulary], or Use [Grimoire] ability known to the victim; the ability begins at a rating of 13, +2 for each mastery the victim possessed in that ability. You may spend 2 hero points to learn any spell known to the victim, starting the ability at 13; you may link these spells to the appropriate talismans possessed by the victim. If you are concentrated in sorcery, you may pay half of these costs.
        If the victim was in a common religion, you may learn any of their talents, charms, feats, or spells for 2 hero points each.
        Any magical abilities you steal from the victim may be improved over time, but you always pay the “Not Concentrated” cost for improvements. For those abilities where there is no “Not Concentrated” cost, you must spend twice the “Concentrated” cost instead. Any abilities gained from Lunar entities are subject to the Lunar cycle.
Tie or Marginal, Minor, or Major Defeat: The victim is dead. You are Impaired (on a Tie or Marginal Defeat) or  Injured (on a Minor or Major Defeat) and require a week to recover. You gain no memories or abilities.
Complete Defeat: Your memories and abilities are lost and replaced by those of the victim. In effect, you have become the victim.

Talismans: Atyari typically make talismans in the shape of small horned skull pendants formed of tarnished silver.
Other Benefits: Apprentices may roll for a random Thanatar gift; upon promotion to adept status, you may roll for another gift and may take another every High Holy Day.
Other Side: Treack Markhor established a node on the Founder Plane. Known as the Athenaeum of Dark Truths, it is constructed out of parts stolen from other nodes. The Athenaeum has secret, hidden connections to other Founder nodes (unbeknownst to those Founders!), and also connects to the Place of Waiting.
Disadvantages: Atyari must still adhere to taboos of spirit relationships they have stolen, or else the spirit will become hostile as normal.

Than
The Headless Spirit
Even diminished, Than had power. When contacted by shamans searching the periphery of well-known myths for new power, he had a new outlet in the world. And as the son of the Devil, Than drew followers—rapacious Orlanthi headhunters who stalked the dark places in the Dawn Age, stealing the heads and powers of rivals and enemies. The Thanics formed a secret group of religious assassins, ritually strangling sacrifices with their garrotes to keep their patron strong and bring closer the day when Than would be made whole again. 
    Reviled and hunted, Thanics remained a persecuted minority on the fringes of the Empire. They learned to operate in secrecy; many found security only in communities of chaotic-tainted folk. Their sign of the coiled garrote became feared, evoking dread from the people of the frontiers. Many times, authorities hunted down the shamans and their circles of followers, but they proved persistent and fanatical. Eventually, the strongholds of Than worship were eliminated. But still, Than waits in the wild places of the Spirit World for mortals to contact him again.

Abilities: Endure Wounds, Garrotte Attack, Than Practice Knowledge, Sense Way when Blind, Spirit Face.
Relationships: Follower of [Than Practitioner].
Virtues: Hate Anti-Chaos Gods, Zealous.
Practice Spirits:
[Chaos] Chaos spirits—Spirits of Tien’s horde (Destroy Daimon 15 to 10W, Extinguish Essence 20, 10 to 5W, Sever Spirit 18 to 12W, ).
[Darkness] Gloom spirits—Spirits of the darkness (Animate Skeleton ritual 20, Create Zombie ritual 10 to 5W, Extinguish Flame 18 to 8W, Smother Sound 16 to 6W, Summon Dehori 17, Wall of Shadows 8 to 7W).
[Death] Guardian spirits—Spirits of dead worshippers (Usually any two abilities like Crushing Grip, Wiresharp Garrote, Disrupt Foe, or Repair Tool: 14 to 1W).
[Spirit] Sacrifice spirits—Spirits of beheaded victims (Abilities specific to the victim, usually at 13 to 1W2. These are always hostile and the practitioner does not have to be related to them to bind them to his service.)
Practice Secret Requirements: Chaos Lore 1W2, Spirit Face 1W2, Than Practice Knowledge 1W2.
Secret: Create Major Head ritual (Chaos magic. The practitioner attempts to bind the spirit, soul, or essence of a helpless individual into their own severed head as a form of gruesome fetish, in a ritual held over the course of Death week in any season.)

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Contest: Create Head
Appropriate Ability: Create Major Head ritual Secret.
Typical Modifiers and Augments: Than Practice Knowledge; ritual magic.
Resistance: The victim’s best ability, even if it does not seem appropriate.
Any Victory: The victim is bound into their own severed, animated head. You must spend 1 hero point to begin a Master of [Victim]’s Head ability at 13; this rating can be raised at a cost of 1 hero point per +1. The head becomes a fetish, with its previous ability ratings intact. You may use the head’s abilities as automatic augments for your own rolls. If you wish to use a head’s magical abilities actively, you may do so by releasing the head as if it were a practice spirit (see HeroQuest page 137); your relevant ability is your Master of [Victim]’s Head ability, and the head is treated as Hostile and resists with its best magical ability. Head entities released in this way do not go to their appropriate Otherworld but remain trapped in the Natural World until they again find their way into their fetish.
        Such heads can last for a while, from about a century (Complete Victory) to a few decades (Major Victory) to only a few years (Minor Victory). Heads which decay or are destroyed release the entities contained within as special Thanatari head ghosts. These insane creatures wander the world, unable to find their way to the Underworld. They usually congregate at Than spirit places and are used as guards. They do not attack anyone with a Worship Thanatar ability, or who possess Than charms or fetishes or Atyari talismans.
        The heads of Than practitioners retain their Master abilities if they are turned into bound heads themselves. Some long-established groups have generations of heads bound to living practitioners through chains of control.
Tie or Marginal, Minor, or Major Defeat: The victim is not bound. Roll your Than Practice Knowledge ability against a resistance of 14; on a tie or any failure, you receive a chaos feature.
Complete Defeat: The victim is not bound. You receive a chaos feature.

Spirit Ally: Members of the Than Practice may receive a Guardian spirit as spirit ally in exchange for a random geas.
Charms and Fetishes: Than charms and fetishes are usually made of the bones of victims chased with tarnished silver. Sacrifice spirits are bound into charms and fetishes made from the victim’s own severed, animated heads; these lesser magic items are called “minor heads” by Thanics and are held in lesser esteem than the full heads created by the Secret, but all ritually severed heads are sacred objects to followers.
Other Connections: Spiritists may roll for a random Thanatar gift; upon promotion to practitioner status, you may roll for another gift and may take another every High Holy Day.
Other Side: Followers of Than go to the Blasted Void, a gloomy mire in the Spirit World that remains where the Spike exploded. Hidden paths lead to the Place of Waiting. Or, using enslaved spirits as guides, followers may journey beyond the edge of the Blasted Void to other parts of the Spirit World, such as the Vale of Four Winds or the Wild Wolf Forest.

Tien
The Severed God
It is clear the Chaos god Tien, son of the Devil, was severed in the God Time. Nevertheless, since Time began, a group was able to recreate the entity to an extent. The combined god is typically called Thanatar, although that name is also used for the entire organization consisting of the three factions: the Horned Society, the Than Practice, and the theistic Cult. To avoid confusion, we will use “Tien” for the theistic cult, and “Thanatar” for the entire religion. 
    Mystery surrounds the origin of the cult. Some say the broo Hero Greegrog retrieved the Skull of Atyar and reconnected it to the Majestic Spirit of Than, recreating the god Tien and being made immortal for his pains. Others say that the Horned Skull still resides in a vault under a ruined city, and that the Broken Council recreated the god as an experiment preliminary to the creation of Osentalka. Due to the organization’s characteristic secrecy, the truth may remain forever unknown.

Abilities: Devotee of Tien or Initiate of Tien, Mythology of Thanatar, Shortsword and Shield Fighting, Soul Vision.
Relationships: Member of [Tien Temple].
Virtues: Fatalistic, Manipulative.
Affinities and Feats:
[Death] Severing (Command Ghost, Sever Soul, Summon Daimon of Reprisal ritual, Survive Beheading [D+20], True Garrote)
[Truth] Knowledge (Find Hidden Knowledge, Sense Weakness, Summon Teaching Daimon ritual)
[Darkness] Shadows (Command Darkness Daimon, Darklight, Replenishing Sleep, Summon Darkness Daimon ritual)
Secret: Summon Specific Guardian ritual (Otherworld magic. The Tien worshipper must travel to the Otherworld to bring back a Thanatari they are trying to resurrect. The quest is difficult, but the Thanatari need not be resurrected into their original body; the only requirement is that seven days cannot have elapsed since death. If the Tien worshipper fails, the Thanatari immediately goes to the Place of Waiting, even if the full seven days have not yet elapsed.)
Other Connections: Initiates may roll for a random Thanatar gift; upon promotion to devotee status, you may roll for another gift and may take another every High Holy Day.
Other Side: Tien worshippers who die are escorted to the Place of Waiting by a cult entity called the Gatherer of Souls. From the Place of Waiting theists may journey to the Darkness Age, or they may follow hidden ways to the Blasted Void or the Athenaeum of Dark Truths.

A Note on Thanatari Magic
Thanatar is a religion for those who wish to possess lore or mastery of skills or magic, but do not wish to do the work to gain such themselves; rather, they steal this power from others. They are greedy and miserly and do not give up magical power that they have stolen.
    Thanatari magic possesses features of all other magical methods. The magic itself is inherently chaotic, and dabbling in Thanatar’s powers is a certain way to acquire a taint or even turn into a chaos horror. Nevertheless, their studies and activities give the Thanatari many advantages.
    Anyone who can convince a current member to sponsor them and can sway the examiners can join the religion. They can treat the Horned Society as just another sorcery school, the Than Practice as just another practice, or the Tien cult as just another cult. For these members, the elements function as normal magical groups, and are subject to concentration as normal. It is worth keeping in mind that the Thanatari religion is an enemy to most other religions, and any follower discovering a cell of Thanatari in their neighborhood is likely to turn them in to the authorities. This fact contributes to the Thanatari virtue of extreme secrecy.
    It is also possible for a follower to concentrate their Thanatari magic. Such followers join the ranks of favored lower-level members in the organization, a group called “The Doomed.” In this case, they may pay the concentrated hero point costs for any Thanatari magic, but must pay double costs for any other kind of magic they wish to learn.
    A follower who has concentrated their Thanatari magic can learn abilities from other branches of the religion. An apprentice of the Horned Society can receive charms for Than spirits or learn affinities from Tien; a spiritist of the Than practice can learn spells from the Horned Society or affinities from Tien; and, an initiate of Tien can learn spells from the Horned Society or receive charms for Than spirits, all paying the concentrated cost for these magics.
    Adepts of the Horned Society can use Than fetishes, using their Worship Thanatar ability [D+10] in place of Than Practice Knowledge when releasing the spirits, or learn feats from Tien. Practitioners of Than can learn Use [Grimoire] abilities and learn spells from those grimoires, or learn feats from Tien. Devotees of Tien can learn Use [Grimoire] abilities, or use Than fetishes, using their Worship Thanatar ability [D+10] in place of Than Practice Knowledge when releasing the spirits.
    The one magic that cannot so easily be stolen is the Cult and Practice Secrets of gods and spirits. Thanatar elite must heroquest mightily for even a fraction of these powers, and the discipline to succeed with such an exertion is foreign to most Thanatari━━this is why they joined a knowledge-stealing religion in the first place!

Thanatari Gifts and Geases
As followers of a Chaos entity, Thanatari of any faction receive random gifts. These are slightly adapted and updated from Nikk Effingham's list.

Thanatar's Gifts

Thanatar's Geases