Gureongdeongdeong Sinseonbi 구렁덩덩신선비
Large monstrosity (shapechanger), neutral good
Armor Class 16 (natural armor)
Hit Points 136 (16d10 + 48)
Speed 30 ft., climb 30 ft., swim 20 ft.
STR 18 (+4) · DEX 14 (+2) · CON 16 (+3) · INT 18 (+4) · WIS 18 (+4) · CHA 15 (+2)
Saving Throws Int +7, Wis +7, Cha +5
Skills History +7, Insight +7, Perception +7, Persuasion +5, Religion +7
Damage Resistances poison
Condition Immunities poisoned
Senses blindsight 10 ft., darkvision 60 ft., passive Perception 17
Languages Common, Draconic, Celestial, Sylvan
Challenge 7 (2,900 XP)
Traits
Shapechanger. As a bonus action, Sinseonbi can magically shed or don his snakeskin, transforming between two forms:
Serpent Form (Large): a huge rat snake with two humanlike arms.
Scholar Form (Medium humanoid): a handsome, robed man.
His statistics remain the same; his gear melds into his body (or appears) with the change. He reverts to serpent form if he dies.
Serpentine Grace. While in serpent form, Sinseonbi can climb difficult surfaces and move through an area only 3 inches wide without squeezing.
Innate Spellcasting. Sinseonbi’s spellcasting ability is Wisdom (spell save DC 15, +7 to hit with spell attacks). He can innately cast the following spells, requiring no material components:
At will: comprehend languages, detect magic, mage hand
3/day each: calm emotions, suggestion
1/day each: clairvoyance, divination
Scholarly Mind. Sinseonbi has advantage on Intelligence (Arcana, History, Nature, Religion) checks, and creatures have advantage on Charisma checks made to convince him with well-reasoned arguments or displays of learning.
Actions
Multiattack (Serpent Form). Sinseonbi makes two attacks: one with Bite and one with Constrict.
Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 7 (2d6) poison damage.
Constrict. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 15 (2d8 + 6) bludgeoning damage, and the target is grappled (escape DC 16). Until this grapple ends, the creature is restrained, and Sinseonbi can’t constrict another target.
Multiattack (Scholar Form). Sinseonbi makes two Quarterstaff attacks or casts one innate spell and makes one Quarterstaff attack.
Quarterstaff. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (1d8 + 7) bludgeoning damage, or 12 (1d10 + 7) bludgeoning damage when used two-handed.
Reactions
Gentle Rebuke (3/Day). When a creature Sinseonbi can see within 30 feet makes an attack roll, he mutters a chastising proverb. The attacker must succeed on a DC 15 Wisdom saving throw or have disadvantage on the roll.
Lore
A scholarly serpent with arms who can take human form.
Gureongdeongdeong Sinseonbi (구렁덩덩 신선비) is a unique figure: unlike most monsters, he is not an antagonist but a positive hero. He is a being who overcomes his animal origins to become the ideal man—a scholar and a husband.
The name itself has a dual nature. Gureongdeongdeong (구렁덩덩) is an onomatopoeic word that evokes the slithering of a huge snake. Sinseonbi (신선비) is made up of sin (신, 神), meaning “divine” or “magical,” and seonbi (선비), the traditional Korean term for a gentleman–scholar.
From Korean Bestiary 5E, p. 48 · Fern Flower Press