Kostchtchie was a 24‑foot (7.3‑meter) tall muscular brute with hunched shoulders and stubby, bowed legs. His head was malformed and his face was flat, ugly, and hairless except for his eyebrows. His skin was a sickly yellow. He always carried with him a massive hammer.
Kostchtchie was a hateful, imperious, and violent dullard who reveled in the frenzy of combat. He was desperate for power and validation, but fearful in the face of powers greater than him. Befitting his title as the "Prince of Wrath," Kostchtchie was renowned for his rages. However, he was petulant and childlike in many respects, and these rages often resembled demonic tantrums. He was known to be easily amused, and would sometimes even spare lesser beings if he found them humorous. Kostchtchie was particularly attached to his massive enchanted warhammer, known as Matalotok.
Kostchtchie was ambitious, but prone to idiotic fixations which distracted him from his larger goals. For example, despite knowing that his realm, the Iron Wastes, was an infinite plane, he was still obsessed with trying to conquer all of it.
Kostchtchie was a relative newcomer among the notable demon lords, and was considered something of an upstart. He ruled the Iron Wastes, the cold and icy 23rd layer of the Abyss, and had ambitions of conquering other layers as well. His primary goal was to rule over all frost giants as their god. He was known to lead raids in both the Prime Material plane and Jotunheim to "liberate" frost giants from their gods, demanding they bow to him or be exterminated. He dismissed any frost giants who refused to bow to him as not "true giants." Supposedly, the knowledge that there were frost giants who did not accept him, or who rejected his worship outright, was a constant source of anguish for Kostchtchie.
Kostchtchie frequently waged war on other layers of the Abyss, and held a strong hatred of other demons. He was known to harbor ambitions of wiping out the entirety of the tanar'ri from existence, and had made great progress toward the extinction of the mavawhan, the ice demons who had been the original rulers of the Iron Wastes before he assumed control.
Even among demon lords, Kostchtchie was known as a fierce and strong fighter. He was possessed of potent magical abilities, such as the ability to bestow curses on his enemies and to cast many innate spells to strip away his opponents' defenses or to bolster his own. However, in combat he often became so caught-up in his battle rages that he completely neglected to use these powers.
Outside of combat, Kostchtchie used his magical abilities to compensate for his mental and physical failings. He possessed the power of telepathy, which he used to supplement the rather narrow number of languages he could speak, and he had the ability to wind walk and teleport, which allowed him to travel great distances that would otherwise be slow-going with his malformed legs.
Kostchtchie derived at least some of his power from his divine hammer Matalatok, which was crafted by Thrym, god of frost giants. For example, he possessed a mastery over cold which was not innate but a power bestowed by the hammer.
Kostchtchie's avatar was historically unable to enter the Material Plane without being summoned via a gate spell, although the demon lord was known to carry an amulet of the planes to compensate for this. Because of this limitation, his aspect had been observed to struggle to balance his blood-lust and ferocity on the battlefield against a certain cautiousness, knowing that he would have trouble returning if slain or otherwise banished back to the Abyss. Merely being in the presence of his aspect could infect mortals with homicidal madness.
By establishing himself as a deity of frost giants, Kostchtchie directly encroached upon the domain of Thrym, though that titan did not take direct action against the demon lord. The dwarven deity Clangeddin Silverbeard considered Kostchtchie, as well as the other evil giant deities, a hated enemy.
Kostchtchie's hatred (and perhaps fear) of women was legendary, and was at least partly driven by his relative powerlessness in the face of certain important women in his life. He was indebted to both Baba Yaga and Iggwilv (a.k.a., Tasha), for giving him immortality and his hammer respectively, and the former was known to have continued manipulating him long into his reign as a demon lord. He also had a history of animosity toward the celestial paragon Gwynharwyf, so much so that he liked for sacrifices made in his name to be done so in her likeness.
He tended to consider most other demons of the Abyss to be his enemies, and had no allies among the other demon lords. He especially hated the demon prince Graz'zt, who had humiliated him in the past, and in his quest for revenge he had begun making overtures of an alliance to Obox-ob.
Kostchtchie was frequently accompanied by his "hounds," a pair of leucrotta that were three times larger than normal. He was very attached to his giant white dragon mount of ancient age, named Svafnir.
Kostchtchie was worshiped by frost giants who had turned away from Thrym, which included many who sought power through learning arcane magic, called his frost mages. Prior to figuring out how to grant cleric spells, his "priests" were wizard cultists called wyrmkin, feared for their ability to summon white dragons. Subsequently, he managed to grant his followers access to the chaos, evil, fury, war, and winter domains. Many high ranking members of the clans and cults that swore allegiance to Kostchtchie undertook efforts to purge themselves of all emotions except wrath, becoming known as a thrall of Kostchtchie.
The most important tenet of Kostchtchie worship was conquest, with his followers tasked with expanding his influence and forcibly converting frost giant clans. A large number of his faithful were members of clans which had been conquered by Kostchtchie or his followers, or who had been abducted by these followers. Frost giants could also invoke him with bloody sacrifices made upon alters of ice with hopes of summoning his aspect. Those followers of his who distinguished themselves in battle were invited to join his massive horde of warriors in the Iron Wastes.
No worship of any deities or powers other than Kostchtchie were permitted in the clans that swore allegiance to the Prince of Wrath, and any "heretics" were dealt with brutally, especially if the heretic was female. Only males were permitted to hold any power within his cult, and often the cult sought to eliminate women from their numbers altogether. If a clan of Kostchtchie worshipers could reasonably sustain its numbers by abducting young males from other tribes, they preferred to sacrifice their females.
Aside from frost giants, Kostchtchie had some scattered cultists among humanoid and ogre barbarian tribes, mostly in colder climates. Some tanar'ri priests were known to pledge themselves to Kostchtchie's service. While Kostchtchie considered these his lesser followers, he believed that they nevertheless had their uses.
Kostchtchie's origins are somewhat shrouded in mystery, largely because of his claim to be a frost giant deity. His preferred story is that he was once a king among frost giants before his apotheosis, but this was an obfuscation meant to legitimize his claim to rule over the giants. Even as a demon lord, he was known to identify as a frost giant, and to became enraged and violent at anyone who suggested he was not.
Kostchtchie was born as a mortal human man, but one who was severely deformed. Spurned by tribes and by women, he was driven to anger and rage. He turned to brutal murder, slaying every woman who ever mocked him and crushing the skull of his former tribe's chieftain with his bare hands.
In time, he was found and mentored by the great witch Baba Yaga. She gave him a set of cursed, nested skulls. Inside the innermost skull—that of a tiny quasit—was hidden a black diamond, and Kostchtchie used dark magic to transfer his soul into this gem, granting himself immortality.
Now unable to be killed, Kostchtchie's body grew both larger and more hideous, until he was the size of a great giant. His tribe grew to the size of a kingdom, and their murderous exploits became infamous and were noticed by powers from other planes of existence. The celestial paragon Gwynharwyf led an army of against his forces, but she was not able to overcome him until she discovered the demonic source of his power. She found and destroyed the skull and its gem, returning his soul to his body so that she could slay him, sending his hateful soul to the Abyss. However, this was only a minor setback for Kostchtchie, whose body was recreated in the Abyss in demonic form.
At some point, the witch Tasha bestowed Kostchtchie with the hammer Matalatok, which had been originally crafted by Thrym, god of frost giants. Kostchtchie used it to dominate a clan of frost giants and would ultimately declare himself a god to them. Kostchtchie led his clan aboard a flying vehicle known as the Ark of Kwalish to plunder treasures from across the planes, including a brutal raid on the City of Brass. The clan was scattered and Kostchtchie banished back to the Abyss during a raid on Scalding Mountain, after which he turned his attention to gaining power within the Abyss.
Kostchtchie first claimed the Iron Wastes by driving the native mavawhan out of the plane's core, and proceeded to wage war on other minor demon lords from across the Abyss, slaying at least three. He also began to antagonized Thrym, such as by capturing and imprisoning his brother, Grjotgard. It was unclear whether his actions against the forces of the Abyss and Thrym were out of his own ambitions of conquest, or if Tasha was pulling his strings.
During this time, Kostchtchie became an unwitting pawn in the endless feud between the Dark Prince Graz'zt and the Queen of the Succubi Malcanthet. Graz'zt infiltrated Kostchtchie's citadel disguised as Malcanthet and seduced the Prince of Wrath, seeking to ultimately pit him against the succubus. Kostchtchie became ashamed and inconsolably furious when the ruse was revealed to him, and proceeded to wreak havoc across half of his own realm before launching a fruitless invasion of Graz'zt's domain of Azzagrat
Around the Year of the Stone Giant, −160 DR, Kostchtchie's hortha was summoned by a cabal from Narfell to assist them in their war against Raumathar, a conflict which would become known as the Great Conflagration. Frost giants gathered under this hortha from the Icerim Mountains and fought on Narfell's side, ultimately conquering Winterkeep and coming into conflict with an avatar of Kossuth.[note 2]
At some point in the mid-to-late 14th century DR, Kostchtchie sent an aspect of himself to the eastern reaches of the Spine of the World mountains to conquer humanoid and giant settlements and to subjugate local frost giants. This aspect completely obliterated at least one small town in the Lands Against the Wall, and came to the attention of a group of adventurers out of Silverymoon.
Sometime prior to the Year of Three Ships Sailing, 1492 DR, Kostchtchie participated in the Blood War by leading an attack into Avernus. In a battle on the shores of the River Styx, he crushed the Nine Hells' 8th Infantry Legion, but was defeated in combat by the archdevil Zariel. His hammer, the mighty Matalotok, was taken by Zariel for her own use, and he was imprisoned in an Avernian ravine which came to be dubbed "Kostchtchie's Maw." From his prison, his howls of rage and demands for release could be heard for miles.
- Kostchtchie is based on Koschei the Deathless from Russian folklore. Koschei is also one of the inspirations for the modern lich as a person who hides their soul in order to attain immortality.
- Ed Stark, James Jacobs, Erik Mona (June 13, 2006). Fiendish Codex I: Hordes of the Abyss. (Wizards of the Coast), pp. 68–69. ISBN 0-7869-3919-2.
- Mike Mearls, Brian R. James, Steve Townshend (July 2010). Demonomicon. Edited by Scott Fitzgerald Gray. (Wizards of the Coast), pp. 122–123. ISBN 978-0786954926.
- Colin McComb (1996). On Hallowed Ground. Edited by Ray Vallese. (TSR, Inc), pp. 175–176. ISBN 0-7869-0430-5.
- James Jacobs (July 2006). “The Demonomicon of Iggwilv: Kostchtchie: Prince of Wrath”. In Erik Mona ed. Dragon #345 (Paizo Publishing, LLC), pp. 21–22.
- Adam Lee, Christopher Perkins (September 17, 2019). Baldur's Gate: Descent into Avernus. (Wizards of the Coast), p. 4. ISBN 0786966769.
- Adam Lee, Christopher Perkins (September 17, 2019). Baldur's Gate: Descent into Avernus. (Wizards of the Coast), p. 105. ISBN 0786966769.
- Carl Sargent (May 1992). Monster Mythology. (TSR, Inc), p. 82. ISBN 1-5607-6362-0.
- Gary Gygax (August 1983). Monster Manual II 1st edition. (TSR, Inc), p. 40. ISBN 0-88038-031-4.
- Frank Mentzer (January 1985). “Ay pronunseeAYshun gyd”. In Kim Mohan ed. Dragon #93 (TSR, Inc.), p. 28.
- Adam Lee, Christopher Perkins (September 17, 2019). Baldur's Gate: Descent into Avernus. (Wizards of the Coast), p. 4. ISBN 0786966769.
- Ed Stark, James Jacobs, Erik Mona (June 13, 2006). Fiendish Codex I: Hordes of the Abyss. (Wizards of the Coast), pp. 135–136. ISBN 0-7869-3919-2.
- Adam Lee, Christopher Perkins (September 17, 2019). Baldur's Gate: Descent into Avernus. (Wizards of the Coast), p. 104. ISBN 0786966769.
- James Jacobs (July 2006). “The Demonomicon of Iggwilv: Kostchtchie: Prince of Wrath”. In Erik Mona ed. Dragon #345 (Paizo Publishing, LLC), p. 24.
- James Jacobs (July 2006). “The Demonomicon of Iggwilv: Kostchtchie: Prince of Wrath”. In Erik Mona ed. Dragon #345 (Paizo Publishing, LLC), pp. 26–27.
- Colin McComb (July 1996). “The Chant of the War”. In Ray Vallese ed. Hellbound: The Blood War (TSR, Inc.), p. 72. ISBN 0-7869-0407-0.
- James Jacobs (July 2006). “The Demonomicon of Iggwilv: Kostchtchie: Prince of Wrath”. In Erik Mona ed. Dragon #345 (Paizo Publishing, LLC), p. 25.
- Mike Mearls, Brian R. James, Steve Townshend (July 2010). Demonomicon. Edited by Scott Fitzgerald Gray. (Wizards of the Coast), p. 127. ISBN 978-0786954926.
- Adam Lee, Christopher Perkins (September 17, 2019). Baldur's Gate: Descent into Avernus. (Wizards of the Coast), p. 224. ISBN 0786966769.
- Bruce R. Cordell, Ed Greenwood, Chris Sims (August 2008). Forgotten Realms Campaign Guide. Edited by Jennifer Clarke Wilkes, et al. (Wizards of the Coast), p. 67. ISBN 978-0-7869-4924-3.
- Carl Sargent (May 1992). Monster Mythology. (TSR, Inc), p. 74. ISBN 1-5607-6362-0.
- Eric L. Boyd (1998). Demihuman Deities. (Wizards of the Coast), p. 58. ISBN 0-7869-1239-1.
- Ed Greenwood (November 1984). “The Ecology of the Leucrotta”. In Kim Mohan ed. Dragon #91 (TSR, Inc.), pp. 16–17.
- James Jacobs (July 2006). “The Demonomicon of Iggwilv: Kostchtchie: Prince of Wrath”. In Erik Mona ed. Dragon #345 (Paizo Publishing, LLC), pp. 28–29.
- Douglas Niles and Michael Dobson (1988). The Throne of Bloodstone. (TSR, Inc), p. 42. ISBN 0-8803-8560-X.
- Colin McComb (July 1996). “The Chant of the War”. In Ray Vallese ed. Hellbound: The Blood War (TSR, Inc.), p. 51. ISBN 0-7869-0407-0.
- Brian R. James, Ed Greenwood (September 2007). The Grand History of the Realms. Edited by Kim Mohan, Penny Williams. (Wizards of the Coast), pp. 55, 57. ISBN 978-0-7869-4731-7.
- Robert Wiese (June 2006). "Steal This Hook! Demon Princes Among Us: Death and Burning Blood". Wizards of the Coast. Retrieved on 2021-06-22.
- Adam Lee, Christopher Perkins (September 17, 2019). Baldur's Gate: Descent into Avernus. (Wizards of the Coast), p. 91. ISBN 0786966769.
- James Jacobs (July 2006). “The Demonomicon of Iggwilv: Kostchtchie: Prince of Wrath”. In Erik Mona ed. Dragon #345 (Paizo Publishing, LLC), p. 32.