Yochlol

Medium Fiend (Demon, Shapechanger), chaotic evil
Armor Class 15 (natural armor)
Hit Points 136 (16d8 + 64)
Speed 30 ft., climb 30 ft.
STR
15 (+2)
DEX
14 (+2)
CON
18 (+4)
INT
13 (+1)
WIS
15 (+2)
CHA
15 (+2)
Saving Throws Dex +6, Int +5, Wis +6, Cha +6
Skills Deception +10, Insight +6
Damage Resistances cold, fire, lightning; bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities poison
Condition Immunities poisoned
Senses darkvision 120 ft., passive Perception 12
Languages Abyssal, Elvish, Undercommon
Challenge 10 (5900 XP)
Shapechanger.
Innate Spellcasting.
Magic Resistance.
Spider Climb.
Web Walker.
Actions
Multiattack.
Slam (Bite in Spider Form).
Mist Form.

This full creature's stat block is not available (not OGL).

Monster Manual
Yochlol