Kostchtchie is called the Prince of Wrath for his destructive rages. Once a mighty Frost giant lord and conqueror of vast stretches of the Elemental Chaos, Kostchtchie is driven to destruction by a near mindless hatred. He has slain several lesser demon lords, and only his limited intellect has prevented him from spreading destruction across the Abyss. To help him along on his path he has Darkvision which helps him pierce the darkness of the Abyss. 
Kostchtchie was once a king among the frost giants. With the help of the Maul of Brutal Endings, he challenged the elders of his frost giant tribe, quickly slaughtering his way to dominance. The Prince of Wrath was said to possess an unnatural talent for leading his tribe to ancient treasures, forgotten tombs, and other locations that harbored powerful magic weapons. He and his followers traveled aboard a flying machine called the Ark of Kwalish, with which he launched a devastating raid against the City of Brass. Kostchtchie's final act as a mortal was a daring raid against the Scalding Mountain, a volcano that rumbles in the Elemental Chaos. He and his followers defeated the devils that guarded that place. Kostchtchie alone entered the volcano's burning core in search of ancient artifacts, but he did not emerge from it. His followers scattered to the winds, and the creatures of the Elemental Chaos breathed a sigh of relief at the end of his reign. That relief was short-lived. Soon after, Kostchtchie appeared in the Abyss, larger and more powerful than ever. The newly made demon lord quickly conquered the Iron Wastes, where huge numbers of his frost giant allies have since joined him in his citadel of ice. From there, Kostchtchie has launched a crusade against the Abyss. Three minor demon lords have already fallen to the Maul of Brutal Endings, and the Prince of Wrath grows stronger each day.
Even compared to other demon lords, Kostchtchie is an avatar of raw destruction. The former frost giant begins each battle in a howling berserker rage that grows in intensity with each injury he takes. The number of demon lords that have fallen to his maul is a testament to Kostchtchie's overwhelming ferocity. Orcus and Demogorgon are said to avoid direct confrontation with the Prince of Wrath for now. Kostchtchie's rivals know that they will face a final reckoning some day, but they are content to allow him to crush lesser abyssal powers until then.
Most folk might welcome the rise of a demon lord bent on slaughtering its own kind. But Kostchtchie is merely a pawn in a much larger game. It was Iggwilv the Witch Queen who set the frost giant king along his path to demonhood, and who continues to manipulate him. With her subtle guidance, Kostchtchie grows more powerful as he wages war against other demon lords. If he ever succeeds in conquering the Abyss, Iggwilv stands ready to snatch away the fruits of his victory. In his youth, Kostchtchie was mocked for his capriciousness and leaden intellect. Although strong, he lacked the cunning of the most powerful berserkers of the frost giant clans. For the crime of killing one of his tormentors, he was banished from his tribe. He wandered the frozen wastes, until one day he came across a small hut built at the base of a towering glacier. There, Kostchtchie met the Witch Queen. Iggwilv had foreseen the frost giant's fate, but saw also that a far greater destiny lay before him. Iggwilv granted Kostchtchie two gifts, one was the mighty Maul of Brutal Endings, and the other was the cacodemon essence of a slain fiend whose intellect she had corrupted. Possessed by this powerful demonic entity in Iggwilv's control, Kostchtchie began his rise to power, compelled to obey her every secret command. At her behest, he rampages through the Abyss to challenge more demon lords, increasing his strength. Eventually, Iggwilv believes that the Prince of Wrath will have the power to crush Orcus and Demogorgon. When that happens, Kostchtchie will command the entirety of the Abyss, at which point, Iggwilv will seize that prize from her thrall, becoming the most powerful being in the cosmos. As yet, no one has confirmed Iggwilv's connection to Kostchtchie. though Graz'zt sees the influence of some greater intellect in the frost giant's tactics. None of the demon lords dare to challenge Kostchtchie directly. Even if the Prince of Wrath were to fall, his foe would be left weak enough that other enemies might quickly overwhelm the victor. Kostchtchie thus grows stronger with each passing year. By banding together, the lords of the Abyss or the gods of the Astral Sea might stop him. However, by the time those always-feuding entities decide to do so, it might already be too late.
Kostchtchie is a relatively new demon lord, and his cults are small and limited in scope. Savage warriors of the frozen tundra pay him fealty, as do creatures that seek raw power and strength in the fury of battle. His former frost giant tribe continues to venerate him, and a growing number of hill giants, ogres, and trolls carry his symbol—a red hammer on a black field.
Out of CombatEdit
Anyone unfortunate enough to encounter Kostchtchie must usually fight him, but the Prince of Wrath sometimes gives his victims a chance to speak before crushing them. Though Kostchtchie is physically powerful, he has the mind of a child, and he is prone to petulant outbursts and fits of rage. Unlike those of most children, Kostchtchie's tantrums can leave whole cities in ruins. Kostchtchie loves flattery. Intimidation can be effective, but can be an overwhelming challenge due to Kostchtchie presence as the Prince of Wrath. If successful, Kostchtchie will respect the winner. Kostchtchie has been known to spare creatures that amuse him and stories or acrobatic feats which entertain the demon lord can calm his rage.
Kostchtchie's wrath and hate are legendary in the Abyss. He has no allies among the other demon lords, but is allowed to rule his realm on the 23rd layer of the Abyss with little interference as a result of his ruinous temper. This realm is utterly and completely under his command, yet Kostchtchie remains unsatisfied with its power. His giants conquer and claim a distant mountain in his name, yet from that mountain's peak the Prince of Wrath can always see one more mountain farther out that remains unclaimed. Worse, he is constantly aware of the simple fact that there exists elsewhere in the multiverse legions of frost giants who do not revere him as their master. The concept that these “lost children” exist enrages Kostchtchie like nothing else, and so he spends much of his time plotting incursions into regions on other planes (particularly the Material Plane). If he can avoid it, Kostchtchie prefers to convert new tribes of frost giants without slaughtering them. His favorite method is to appear to a new tribe, slay their current jarl, and then lead the tribe on a gruesome war against their enemies. If the tribe is slaughtered, Kostchtchie dismisses them as failures—not “true” giants. If they succeed, they are rewarded with entrance into the Iron Wastes, where the tribe can serve him eternally. Of course, these raids have done much in establishing his reputation as a war monger among those peoples he incites the giants to assault. Kostchtchie has a particular hatred of frost giant tribes who worship other deities and often launches assaults on these tribes simply to discourage such heretical acts.
Most of Kostchtchie's cultists are frost giants, although it's not unheard-of for particularly brutal tribes of humanoid or ogre barbarians to venerate him as well. These cultists rank lower in Kostchtchie's eyes simply because of their smaller stature, although he does begrudgingly admit that a tribe of fiercely loyal humanoid or ogre barbarians can have its uses. Clerics of Kostchtchie have access to the domains of Chaos, Evil, Fury, and Winter. Kostchtchie's favored weapon is the maul. His symbol is a hammer rimed in bloody ice.