based on D&D 5th Edition
Huge  Fiend Demon, Chaotic Evil

Armor Class 19  (natural)
Hit Points 262  (21d12+126)
Speed 40 ft. , fly 80 ft. , swim 20 ft.

26  (+8) 15  (+2) 22  (+6) 20  (+5) 16  (+3) 22  (+6)
Saving Throws Str +14, Con +12, Wis +9, Cha +12
Damage Resistances Bludgeoning, Frost, Lightning, Piercing, Slashing
Damage Immunities Fire, Poison
Condition Immunities Poisoned
Senses truesight, passive Perception 13
Languages Abyssal, Telepathy
Challenge 19  (22000 XP)
Fire Aura. At the start of each turn each creature adjacent takes 10 (3d6) fire damage. Creatures touching or using melee attacks within 5 ft. take 10 (3d6) fire damage.
Death Throes. When destroyed it explodes and each creature within 30 ft. must make a DC 20 Dexterity save or take 70 (20d6) fire damage, half damage on successful save..
Teleport. Teleport 120 ft. to unoccupied space it can see.
Magic Resistance. Has advantage on spell and magic saving throws.
Magic Weapons. Weapon attacks are magical. .
Multiattack. Make one longsword and one whip attack
Longsword. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 21 (3d8+8) slashing damage. Critical hits do triple damage
Longsword+. plus 13 (3d8) lightning damage. Critical hits do triple damage
Whip. Melee Weapon Attack: +14 to hit, reach 30 ft., one target. Hit: 15 (2d6+8) slashing damage.
Whip+. plus 10 (3d6) fire damage. DC 20 strength saving throw or pulled adjacent