Unusual Yuan-Ti Pureblood Commoner

Chameleon Skin. The Commoner has advantage on Dexterity (Stealth) checks made to hide.

Magic Resistance. The Commoner has advantage on saving throws against Spells and Other Magical Effects.

Unusual Ability. The Commoner Chooses one or more of the following Abilities: Bite, Chameleon Skin, Shapechanger, or Shed Skin. 

Bite. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 2 (1d4) Piercing damage plus 3 (1d6) Poison damage.

Club. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 2 (1d4) bludgeoning damage.

Shapechanger. The Commoner Polymorphs into a Medium Giant Poisonous Snake or into a Large Constrictor Snake or back into it's true form, it's statistics Remain the same in each form except for the size change noted, it doesn't change Form if it dies.

Innate Spellcasting. The Commoner can Cast the Following Spells, Intelligence is it's Spellcasting Ability (DC 11):

At Will: Animal Friendship (Snakes Only), Poison Spray

Shed Skin (1/Day). When the Commoner is Grappled, in shackles or otherwise Restrained it can shed its Skin to Free itself, additionally it can spend 1 Minute eating it's shed skin to regain 4 Hitpoints.