Sources
CR
Type
Size
Alignment
Movement

Fury of Kostchtchie

Huge Fiend (demon), Chaotic Evil

Armor Class 16 (natural armor)
Hit Points 216 (16d12 + 112)
Speed 40 ft.
STR
26
+8
DEX
10
+0
CON
25
+7
INT
10
+0
WIS
12
+1
CHA
11
+0
Saving Throws CON +12, WIS +6
Skills Athletics +13, Perception +6
Damage Resistances fire, lightning, poison
Damage Immunities cold
Condition Immunities Charmed, Frightened, Poisoned
Senses darkvision 120 ft., passive Perception 16
Languages Abyssal, Giant
Challenge 14 (11,500 XP)

Traits

Chilling Aura. A creature that starts its turn within 10 feet of the fury must succeed on a DC 20 Constitution saving throw or take 11 (2d10) cold damage.

Magic Resistance. The fury has advantage on saving throws against spells and other magical effects.

Actions

Multiattack. The fury makes two Fist or Rock attacks.

Fist. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit:17 (2d8 + 8) bludgeoning damage plus 10 (3d6) cold damage, or 17 (5d6) cold damage if the target took damage from the fury's Chilling Aura since the end of the fury's last turn.

Rock. Ranged Weapon Attack: +13 to hit, range 60/240 ft., one target. Hit:30 (4d10 + 8) bludgeoning damage.

Bonus Actions

Charge. The fury can move up to its speed toward an enemy it can see.

Lore

Frost giants who struggle to rise in their ordning, along with those who reject Annam and his children, sometimes turn to the worship of the demon lord Kostchtchie. In the myths of these giants, Kostchtchie was once a frost giant of such tremendous might that he slew a demon lord in single combat, claimed its Abyssal realm for himself, and now waits for other frost giants to join him in conquering the rest of the Abyss.