TEXT: 
  The Serpent Men are humanoid reptiles who possess the
  head of a snake. They are magical creatures with many
  abilities, but the one they use most commonly is their ability
  to cast illusions upon themselves in order to appear as a
  regular human. According to some legends, the spirit of a
  mortal killed by a Serpent Man becomes his slave upon death.
  Scions of the Great Serpent. Originally created by
  the Great Serpent, who was actually the Great Old One Yig,
  the Serpent Men were birthed into this world in aeons past.
  Building a mighty empire, this first civilization fell with the
  rise of the dinosaurs over 225 million years ago. Much later, a
  mere 20,000 years ago, the Serpent Men rebuilt their empire
  and ruled over the human race, but were eventually toppled by
  their slaves in a long war. They then proceeded to infiltrate
  human society where they again ruled their former servants,
  but this time from behind the scenes. Ultimately, they were
  discovered and cast out again, and thus the Serpent Men
  passed from reality into legend.
  Modern Serpent Men. From the overworld, the remnants
  of the defeated civilization migrated to the cavern
  of Yoth beneath K'n-yan in modern-day North America. Slowly
  rebuilding their society, the Serpent Men this time brought
  about their own downfall by abandoning their worship of Yig
  in favor of another Great Old One known as Tsathoggua.
  Seeing this, Yig cast down their cities and laid a curse on the
  Serpent Men, forcing them to flee their new home and scatter
  across the globe.
  This is unofficial Fan Content permitted under the Fan Content Policy. Not approved/endorsed by Wizards. Portions of the materials used
  are property of Wizards of the Coast. ©Wizards of the Coast LLC.
  
  Medium humanoid (serpent man), neutral evil
  Armor Class 15 (natural armor)
  Hit Points 26 (4d8 + 8)
  Speed 30 ft.
  STR
  DEX
  CON
  INT
  WIS
  CHA
  11 (+0) 16 (+3) 14 (+2) 13 (+1) 13 (+1) 12 (+1)
  Skills Arcana +3, Deception +3, Perception +3,
  Stealth +7
  Damage Immunities poison
  Condition Immunities frightened, poison
  Senses darkvision 60 ft., passive Perception 13
  Languages Common, Deep Speech
  Challenge 1 (200 XP)
  Innate Spellcasting. The serpent man's spellcasting
  ability is Charisma (spell save DC 11). The serpent
  man can innately cast the following spells, requiring
  no material components:
  At will: disguise self 
  1/day: charm person
  Actions
  Multiattack. Bite. Melee Weapon Attack: +5 to hit,
  reach 5 ft., one target. Hit: 5 (1d4 + 3) piercing
  damage plus 2 (1d4) poison damage. If the target is
  a creature it must succeed on a DC 12 Constitution
  saving throw or become poisoned. While poisoned
  the target has disadvantage on Constitution saving
  throws.
  1
  
  This is unofficial Fan Content permitted under the Fan Content Policy. Not approved/endorsed by Wizards. Portions of the materials used
  are property of Wizards of the Coast. ©Wizards of the Coast LLC.
  
  
  Medium humanoid (serpent man), neutral evil
  Armor Class 15 (natural armor)
  Hit Points 102 (12d8 + 48)
  Speed 30 ft.
  STR
  DEX
  CON
  INT
  WIS
  CHA
  14 (+2) 16 (+3) 18 (+4) 17 (+3) 17 (+3) 18 (+4)
  Saving Throws Wis +6, Cha +7
  Skills Arcana +3, Deception +3, Perception +3, Stealth
  +7
  Damage Immunities poison
  Condition Immunities frightened, poison
  Senses darkvision 60 ft., passive Perception 13
  Languages Common, Deep Speech, Draconic
  Challenge 6 (2,300 XP)
  Innate Spellcasting. The serpent man's spellcasting ability
  is Charisma (spell save DC 11). The serpent man can
  innately cast the following spells, requiring no material
  components:
  At will: disguise self, false life, levitate, speak with   dead
  1/day: bane (uses a spell slot), compulsion (uses a
   warlock spell slot), charm person, confusion
  Spellcasting. The serpent man is a 12th-level spellcaster.
  Its spellcasting ability is Charisma (spell save DC 15, +7
  to hit with spell attacks). It regains its expended spell
  slots when it finishes a short or long rest. it knows the
  following warlock spells:
  Cantrips (at will): eldritch blast (fires 3 bolts), friends,
    mage hand, minor illusion* 
  1st-5th level (3 5th-level slots): charm person, detect
    thoughts, dimension door, dominate person, dream,
    enthrall, fear, hex, hold person, hypnotic pattern,
    suggestion
  Whispering Aura. At the start of each fo the serpent
  man's turns, each creature of its choice within 5 feet of
  it must succeed on a DC 15 Wisdom saving throw or
  take 10 (3d6) psychic damage.
  Actions
  Multiattack. The serpent man makes two attacks with its
  scimitar and one attack with its bite.
  Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one
  target. Hit: 5 (1d4 + 3) piercing damage plus 2 (1d4)
  poison damage. If the target is a creature it must
  succeed on a DC 12 Constitution saving throw or
  become poisoned. While poisoned the target has
  disadvantage on Constitution saving throws.
  Scimitar. Melee Weapon Attack: +6 to hit, reach 5 ft.,
  one target. Hit: 6 (1d6 + 3) slashing damage.
  2
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/5th Edition (5e)/3rd Party/DmDave/Serpent Men of Yig.pdf